(n.) a flock of small birds
Why just call a group of birds a flock, when you can call it a dissimulation?
That’s not the only meaning of this word, of course, as the noun dissimulation has been in use in English since the 1300s as a word for the act of dissembling, disguising, or in some way concealing something. In that sense, it derives ultimately from the Latin verb simulare, meaning ‘to make like’ or ‘copy’—or, by extension, ‘to feign’.
It’s probably through the notion of a flock of birds attempting to bamboozle a predator or hunter by seeming to fly together as a single unit that this word was chosen as a term of venery (better known as a collective noun) for a flock of small birds in the fifteenth century. The Book of St Albans, published in 1486, was a collection of essays and treatises on all manner of gentlemanly pursuits, including ‘hunting, hawking, and cote d’armour’.
It was in those chapters on hunting and falconry that the St Albans included a list of fanciful and humorous groups terms for various people, animals and birds; it is here, in fact, that many of our most best-remembered and most idiosyncratic collective nouns—like a business of ferrets, a labour of moles and a shrewdness of apes—were first set down. And there too was this term, which has remained in occasional (and often fairly non-serious) use ever since.