Early 17th century; earliest use found in Randle Cotgrave (fl. 1587–?1630), lexicographer. From nock + -andro, of uncertain origin, but perhaps from ancient Greek ἀνδρ-, ἀνήρ man, in order to distinguish it from a woman's nock.
Definition of nockandro in US English:
nockandro
nounnɒkˈandrəʊ
rare, archaic
The buttocks; the anus.
Origin
Early 17th century; earliest use found in Randle Cotgrave (fl. 1587–?1630), lexicographer. From nock + -andro, of uncertain origin, but perhaps from ancient Greek ἀνδρ-, ἀνήρ man, in order to distinguish it from a woman's nock.