A noxious or mischievous animal; especially, noxious little animals or insects, collectively, as squirrels, rats, mice, worms, flies, lice, bugs, etc.
Hence, in contempt, noxious human beings.
any of various small animals or insects that are pests; e.g. cockroaches or rats
Objectionable pests, usually of a small size, such as flies, mice, and rats, etc..
Any undesirable or disturbing offender such as flies, lice, fleas, cockroaches, ticks, mice, rats, weasels.
Vermin is a term applied to various species regarded as pests or nuisances, and especially to those associated with the carrying of disease. Since the term is defined in relation to human activities, which species are included will vary from area to area and even person to person. The term itself derives from the Latin vermis, meaning worm, and originally had reference to the vermiform larvae of certain insects, many of which infest foodstuffs.
In the Dungeons & Dragons fantasy role-playing game, vermin is a type of creature, or "creature type". Vermin can be any insects, arachnids, other arthropods, worms, and similar invertebrates, including giant versions of normal creatures. Most vermin are mindless.