We sometimes encounter people who are fond of correcting anyone who uses decimate in any but the original ‘Roman military punishment’ sense, yet these adherents to historical accuracy seem to not take issue with any number of everyday words. Take, for example, triumph.
What it meant: an ancient Roman ceremonial in honor of a general after his decisive victory over a foreign enemy beginning with his entrance into the city preceded by the senate and magistrates, the spoils, and the captives in chains and followed by his army in marching order and ending with sacrificial offerings and a public feast
In ancient Rome different types of victories called for different types of celebrations; a triumph was awarded to generals who had achieved notable victories. You may, of course, still describe your own small personal victories as a triumph, even if they are not followed by sacrificial offerings and public feasting.
What it meant: a ceremony attending the entering of Rome by a general who had won a victory of less importance than that for which a triumph was granted
If one was a Roman general and had won some battles, but not dealt enemies enough of a defeat to be awarded a triumph, then one might be given an ovation. This sense dealing with Roman military history was the initial meaning in English, but somewhere in the past few centuries the primary meaning of the word has shifted to “an expression or demonstration of popular acclaim especially by enthusiastic applause.”
What it meant: either of the two joint chief magistrates of the Roman republic
When consul came into English use in the 14th century, it was used with specific reference to Roman magistrates; the word may be traced back to the Latin consulere (“to consult”). In current use, consul most often is found with the meaning of “an official appointed by or with the authority of a government to reside in a foreign country to represent the interests of citizens of the appointing country (as in commerce).”
What it meant: a chief magistrate appointed in emergencies and given absolute authority by the senate of ancient Rome
Nowadays, dictator tends to be used to refer to any sort of autocratic leader with complete governmental or institutional power. In early use the word was specifically used in describing the magistrates of ancient Rome who were given (temporary) complete authority by the Senate.
What it meant: the marketplace or public place of an ancient Roman city consisting of an open place or square surrounded by shops or in later times by public buildings or ornamental structures (as colonnades) and forming the center of judicial and public business
In current English the word forum is often found in extended use, with meanings such as “a public meeting or lecture involving audience discussion” or “a program (as on radio or television) involving discussion of a problem usually by several authorities.” When first adopted from Latin into English, forum (which may be pluralized as either forums or fora) specifically referred to the marketplace or public space of an ancient Roman city.
What it meant: a member of the highest class of official diviners of ancient Rome
Augur is rarely used in English today in its original sense, which was as a noun for an official diviner (soothsayer) of ancient Rome (which raises the question of whether there were also unofficial soothsayers). Currently augur is most often found used as a verb, meaning “presage” or “foretell from omens,” with no particular references to Rome, or whether the foretelling being done is official or not.
What it meant: a large oblong or circular structure similar to an amphitheater and enclosed by tiers of seats on three or all four sides and used for athletic contests, exhibitions of horsemanship or in ancient times chariot racing and public especially gladiatorial spectacles
Circus comes from the Latin, in which it means “circle” or “circus.” In its earliest English use (14th century) the word referred to the spectacles of Ancient Rome. Subsequent to this circus has taken on addition meanings, including “a public spectacle” and “something suggestive of a circus (as in frenzied activity, sensationalism, theatricality, or razzle-dazzle).”
What it meant: a person corresponding nearly to the guardian of English law and appointed to manage the affairs of a person past the age of puberty while he is a minor or of any such person when legally incompetent (as a spendthrift or a lunatic)
When curator came into English use in the 15th century, the above definition was specifically applied to contexts of Roman law, the word’s first meaning. Since then curator has taken on numerous other senses, including “a groundsman in the sport of cricket” and “one in charge of the exhibits, research activities, and personnel of a museum, zoo, or other place of exhibit.”
What it meant: a member of one of the original citizen families of ancient Rome
In current use patrician is most often found as an adjective (often with the meaning “of, relating to, having, or characterized by high birth, rank, or station”). When the word came into English use in the 15th century, it initially was as a noun, solely in reference to those Roman families who, until about 350 B.C., occupied the offices of senator, consul, and pontifex.
What it meant: to select by lot and kill every tenth man of
The English language is filled with words which have changed meaning, or taken on new shades of meaning; decimate is just one of thousands of words which have dropped a sense, and insisting that those who fail to observe this obsolete sense do so in error tends to mark you as an irritating pedant, rather than as a dutiful historian of language. If you would like a longer explanation of why this nit-picking captiousness is bothersome you may find it here.