Definition of piss:
(n) :
Urine; alcoholic beverage, especially of inferior quality
"1611 Monster, I do smell all horse-piss; at which my nose is in great indignation. -- Shakespeare, The Tempest, Act 4, Scene 1."
(interjection) :
used as a euphemism for
fuck
(v) :
to urinate; to discharge as or with the urine