"ant," late 14c. (early 14c. as a surname), from pyss "urine" (said to be in reference to the acrid smell of an anthill) + mire "an ant" (mid-13c., early 13c. as a surname), perhaps from an unattested Old English word or from Old Norse maurr "ant" (cognate with Swedish myra, Danish myre, Middle Dutch miere, Dutch mier, Crimean Gothic miera "ant"), from PIE base *morwi- (see Formica (2)). Compare pissant, also early Dutch mierseycke (from seycke "urine"), Finnish kusiainen (from kusi "urine").
He is as angry as a pissemyre,
Though þat he haue al that he kan desire.
Applied contemptuously to persons from 1560s.