'Pet cock' definitions:

Definition of 'Pet cock'

From: GCIDE

pet \pet\, a. Petted; indulged; favorite; admired; cherished; as, a pet child; a pet lamb; a pet theory; a pet animal. [1913 Webster]
Some young lady's pet curate. --F. Harrison. [1913 Webster]
Pet cock. [Perh. for petty cock.] (Mach.) A little faucet in a water pipe or pump, to let air out, or at the end of a steam cylinder, to drain it. [Also spelled petcock.] [1913 Webster]