(n.) a lucky coin
Thanks to their instantly recognisable call (and their, shall we say, questionable parenting techniques), cuckoos have made themselves conspicuous enough to become subject to all kinds of fantastical theories from ancient folklore.
According to one legend, for example, the birds are said to herald rain if they’re spotted on a sunny day. Another claims that the birds are attracted to other creature’s nests because the mother birds drink egg yolks to help clear their voices and louden their calls. And, long before we fully understood and appreciated the migration of birds, one old English tradition claimed that cuckoos disguised themselves as (or else, entirely transformed themselves into) hawks and other birds of prey during the winter months, before shedding their disguises in the spring. We have some strange relatives here at HH, clearly.
To that list we can add this word too: a cuckoo-penny is a lucky coin.
Another local bit of English folklore claims that cuckoos always return to Britain on 14 April each year. On or around that date, according to the rule, everyone should carry a small amount of change in their pocket known as a cuckoo-penny, so that when they hear their first cuckoo of the year, they can turn the coin over in the pocket, hidden out of sight of the bird, and thereby guarantee that the remainder of the year will be a prosperous one:
When the time for [the cuckoo’s] arrival draws near—the 14th of April—all ears are a-cock for the first note, and care is taken that no pocket shall be absolutely devoid of coins of the realm of some value or other. On the 12th of April last, a farmer’s man came to me to borrow “only a hap’ney,” for he expected, “th’ cuckoo,” and “mus’ner be wi’ert a coin” ... in case he should hear it.
Long Ago: A Monthly Journey of Popular Antiquities (1873)