We all know that doctors of old once used leeches, but how many are aware that until around the 16th century that doctors were leeches, at least in English speaking areas? And nor was it a term of criticism either - in fact the word had a distinguished and worthy pedigree all the way back to Gothic and proto-German (lekeis) and beyond, and is believed to have originate from an Indo-European root "leg-" where it denoted both collecting and learning. In fact it is from the latter application semantically that later languages invented another swathe of words which have also filtered down to English in the form of "legible", "lecture", "lectern" etc. As semantic strands run, this is one of history's more edifying examples indeed!

So what went wrong, and why would we now recoil somewhat in shock if a young son or daughter answered with enthusiasm when asked what they wanted to be when they got older that their earnest desire was to become a leech?

In this case the answer lies in coincidence rather than semantic shift, or indeed some long deeply held suspicion about medical practitioners (though in times past this could very well have been amply justified). We're not quite sure about any long pedigree dating back to Indo-European roots but we do know that Old English employed a word "læce" (in Kent we know of "lyce") to indicate the literal bloodsucker (as opposed to the figurative one we are familiar with today from reading medical bills). This "c" was pronounced as we do now the "ch" in "leech". Moreover the word co-existed with our friend the doctor, who at that time in Old English was going under the name of "læke". The "k" was hard, and sounded almost like a "g". Two different words. In fact in Norse today the doctor is still in fact called a "lege".

But then, when the "lækes" started using "læces" to treat all ills ranging from ingrown toenails to split personality their patients, quite understandably, began to see a rather obvious parallel between the two distinct semantic strands they were faced with and, even less surprisingly, saw no reason why the same word shouldn't apply to both. The "k" softened to "ch" as the attitude of the speaker hardened in tandem and, for a period of almost a thousand years leeches found themselves in competition with leeches over how many people could be bled dry or cured while paying through the nose (hopefully not literally).

In semantics this is called a "deceptive" lexeme - it appears to have happened totally coincidentally (if doctors hadn't actually used leeches in their treatments then the overlap would never have occurred) - or sometimes an "encouraged" lexeme (the doctors invited the overlap to be made so it was bound to happen, it just took a little prompting to do so).

The lexeme held sway right up to the 17th century when use of "physick" and then "doctor" gradually came into vogue, more or less in line with the growth of colleges set up to train people in the profession. As their self-opinion grew so did their inclination to discourage association in name terms with one of their most common tools, and especially one with so coincidentally accurate an allegorical role in things.

However I was wondering if there are are any more such "deceptive" lexemes out there? Ones which have actually survived to this day?

I can't answer that off the top of my head, though I am fairly certain there are some. However it is your first clause I was going to comment on. It isn't just doctors of old who use leeches - they are used in hospitals now. I am certain I read an article about their use in the hospital not far from where I live, though I can't find it now. But I did find an article from the Los Angeles Times talking of their use and saw a sentence in an article about their use in Indian Kashmir that said, "In 2004 use of blood-sucking leeches was approved by the US government as a tool for healing skin grafts or restoring circulation." And as sentence somewhere else that spoke of their use in NZ hospitals.

It is a comeback rather than a continuation though. This article from a 19th century newspaper talks of how their use had dramatically declined. (The bit about leeches is down half a dozen paragraphs.)

http://paperspast.natlib.govt.nz/cgi-bin/paperspast?a=d&d=ST18970315.2.8&l=mi&e=-------10--1----0--

I've always wondered about the strange use of "gaffer" - word you see in the list of credits at the end of films.

But no, not really relevant for this question. A gaffer is the correct word for the chief electrician or lighting technician in a film crew. Nothing to do with mistakes or blunders. It comes from the old word for grandfather or aged rustic, even a respected village elder - hence the more understandable slang use of "gaffer" in any trade or profession to mean "boss". I had hoped for boss to mean "blunderer" too, but no. A gaff was originally a huge hook used in fishing, so no obvious connection there.

Again not really relevant, but an odd expression that has survived - the "best boy" in a film crew. He is the gaffer's assistant. You'd expect the term to have been banned or altered, but it's somehow slipped through the PC gender net.

(Maggots have staged a comeback, too; they are being successfully used to clean up infected wounds. Maggots on the NHS - very cheap, I suppose.)

Edit 1: re maggots http://news.bbc.co.uk/1/hi/england/north_yorkshire/4163789.stm

Edit 2: Found out last night that gaff, besides a hook, was a sailing term - to do with rigging. The link with the film industry is to do with getting at overhead lighting equipment: gaff "a means of access to utility poles in climbing". So a "gaffer" in a film studio combines being the boss with climbing up to get at lights - I'm still rather muddled, though.

I've often wondered at the etymology of the word 'germ' as in a pathogen and if this is at all related to the proper noun 'German'. I'm pretty sure that I've heard people refer to Germans to as 'the Germs' in a derogatory/comedic manner. But could it be that they're not being as clever as they think they are but are actually re-enforcing an existing etymological origin.

The origin of the word germ is seemingly the Latin 'germen' meaning a shoot, a sprout or a bud - while the Latin word 'germanus' (lower case 'g') refers to an offshoot or a sucker or a sapling. It also suggests kinship which is where the word germane finds its origin. It would seem to be the tiniest of linguistic steps to turn a lower case 'g' to an upper case 'G' but linguists are divided on this.

In the English language the word 'germ' originally had a wholesome connotation as in wheat germ etc. It was only following the publication of the Antiseptic Principle Of The Practice Of Surgery by Joseph Lister in 1867 that the term 'septic germs' or just 'germs' for short began entering common parlance with a negative connotation. And 1867, of course, was only 4 years before the unification of Germany. An untimely co-incidence perhaps?

According to this Viz, the English word German is from J Caesars use of the word Germani to desegnate the group of tribles living in northeastern Gaul.

http://www.etymonline.com/index.php?allowed_in_frame=0&search=German&searchmode=none

Caesar cited the term as already in use amongst Gallic people. Alexandra von Dyhrn suggested that this Celtic expression which Caesar attempted to approximate in Latin was actually one which in all likelihood corresponded to the Indo-European "sjen-" root indicating tribe or root, exactly the same as that from which the Latin "genus" had also been derived. In Irish there is still an archaic word "cine" (nation, people) which is thought to be a derivative also of the same ancient Celtic term.

"Germ" as we understand it, is also a word which originated from the Indo-European "sjen-", so in that sense while we do not have a lexeme as such we most definitely have the evidence of one from the past preserved in the two distinct terms.