Cuckoo

It is said that on this day (ah, sweet harbingers of spring!) the cuckoo makes its appearance. But careful what one wishes for, eh? For “cuckoo”, the bird that lays its eggs in the nest of another, is the root of “cuckold”:

Cuckoo, cuckoo – O word of fear,
Unpleasing to a married ear.

(Thanks to the Book of Days.)