Etymologists generally have regarded the name of the bloodsucking animal as the same word with leech a physician, the assumption being that the animal received its name from its use as a remedial agent. But the early forms, both in English and Low German, show that the words are originally unconnected. The English for medicus was in the tenth century l[’[ae]]ce or l[’e]ce, and in the thirteenth century leche; the word for sanguisuga was in the tenth century lyce, and in the thirteenth century liche. According to phonetic law the latter word should have become litch in modern English; but it very early underwent a punning alteration which made it homophonous with the ancient word for physician. The unfortunate consequence is that the English language has hopelessly lost a valuable word, for which it has never been able to find a satisfactory substitute.
On this very difficult question the attitude of a careful English speaker is shown in the following extract from a letter addressed to us:
’I find that I do not naturally distinguish metal and mettle in pronunciation, tho’ when there is any danger of ambiguity I say metal for the former and met’l for the latter; and I should probably do so (without thinking about it) in a public speech. In my young days the people about me usually pronounced met’l for both. Theoretically I think the distinction is a desirable one to make; the fact that the words are etymologically identical seems to me irrelevant. The words are distinctly two in modern use: when we talk of mettle (meaning spiritedness) there is in our mind no thought whatever of the etymological sense of the word, and the recollection of it, if it occurred, would only be disturbing. So I intend in future to pronounce metal as met[e]l (when I don’t forget). And I am not sure that met[e]l is, strictly speaking, a “spelling-pronunciation”: It is possible that the difference in spelling originated in a difference of pronunciation, not the other way about. For metal in its literal sense was originally a scientific word, and in that sense may have been pronounced carefully by people who would pronounce it carelessly when they used it in a colloquial transferred sense approaching to slang.
’The question of principal and principle is different. When I was young, educated people in my circle always, I believe, distinguished them; so to this day when I hear principal pronounced as principle it gives me a squirm, tho’ I am afraid nearly everybody does it now. That the words are etymologically distinct does not greatly matter; it is of more importance that I have sometimes been puzzled to know which word a speaker meant; if I remember right, I once had to ask.