This post is one in a series about The Negative Canon.
Some of those who like to show that they recall a little of the Latin they may have once been taught love to tell us that decimate should only be used to mean ‘reduce by one tenth’. If they are particularly zealous, they will tell us that we should even reserve the word for killing every tenth soldier pour encourager les autres.
The first definition of the first conjugation Latin verb decimo in Lewis and Short’s ‘A Latin Dictionary’ is, indeed, ‘To select by lot every tenth man for punishment, to decimate’, with the comment that the word is post-Augustan, but that the practice itself occurred much earlier. This, too, is the earliest meaning in English attested in the OED:
To select by lot and put to death one in every ten of (a body of soldiers guilty of mutiny or other crime): a practice in the ancient Roman army, sometimes followed in later times.
It’s supported by this citation from John Dymmok’s ‘A Treatise on Ireland’ published around 1600:
All . . . were by a martiall courte condemned to dye, which sentence was yet mittigated by the Lord Lieutenants mercy, by which they were onely decimated by lott.
Subsequent meanings are given as ‘To exact a tenth or a tithe from; to tax to the amount of one-tenth’, and ‘To divide into tenths, divide decimally.’ These are consistent with Lewis and Short’s further definitions of the Latin word ‘To cause to pay tithes, to collect tithes from a person’ and ‘To select the tenth part as an offering, to pay tithes of anything’, supported by references, among others, the Vulgate Bible.
The OED’s definition 4a, however, is:
To kill, destroy, or remove one in every ten of
and 4b is:
(rhetorically or loosely) To destroy or remove a large proportion of; to subject to severe loss, slaughter, or mortality.
This doesn’t go quite as far as the OED’s contemporary companion, Oxford Dictionaries Online, where the first definition is ‘Kill, destroy or remove a large proportion of’ and ‘Drastically reduce the strength or effectiveness (of something)’.
It is this more general use that some object to. In ‘Mind The Gaffe’, R L Trask advises unequivocally ‘you should never use decimate to mean “annihilate” or “destroy”’, while in ‘The Penguin Guide To Plain English’, Harry Blamires writes of the ‘misuse [which] occurs when the word decimate is seemingly confused with some other word such as devastate.’ (He is also concerned that decimate is used to mean to reduce to one-tenth rather than by one-tenth, but I’ve not seen anyone else make that complaint.)
What all this amounts to is that those who want decimate to have something to do with the number ten fall prey to the Etymological Fallacy. A word rarely means now what it once did. Those who want decimate to remain faithful to its Latin root, or at least to its earlier meanings in English, are extremely selective. Why do they not insist on using complexion to mean ‘temperament’ rather than ‘skin’, or strange to mean ‘foreign’ rather than ‘unusual’, or cretin to mean ‘(Christian) creature’ rather than ‘idiot’? Vocabulary in particular seems to show the arbitrary nature of those items that are picked from the Negative Pool to enter the Negative Canon.