any of a large class of invertebrate animals with a well-defined head, thorax, and abdomen, three pairs of legs, and typically one or two pairs of wings: class Insecta
A fly, sir, may sting a stately horse and make him wince; but the one is but an insect, and the other a horse still — Dr Johnson
loosely, any of various small invertebrate animals that do not belong to the insect class but that superficially resemble insects, e.g. woodlice and spiders
a worthless or insignificant person
[Latin insectum, neuter of insectus, past part. of insecare to cut up, from in-2 + secare to cut; because of the insect's segmental body]