The cuckoo bird is so named for its one-note song, which in Middle English was represented as cuccu in imitation. Figurative use of cuckoo, which exists as an adjective meaning "crazy" or "weak in intellect or common sense," and as a noun for a person who can be described as such, may be an allusion to the bird's eponymous (and monotonous) call. But it may also be inspired by a peculiar habit exhibited by some species, in which a female will lay her eggs in the nest of another bird, to be hatched by that bird. In Old French, the name of the bird, cucu, also refers to a husband whose wife is unfaithful. That sense is believed to come from the female cuckoo bird's habit in some species of changing mates, or to the same egg-laying habit that influenced English figurative use. Cucu is also the source of English cuckold.