Green’s Dictionary of Slang

1. the penis.

1768		Gentleman’s Bottle-Companion 39: With holy love he rolls his eyes. Yet views his stout man Thomas rise.
1785		Grose Classical Dict. of the Vulgar Tongue.
1836		‘The Patent S--t-Pot’ in Cockchafer 31: She told Kate how she long’d for young Thomas so fair.

2. generic name for a liveried servant.

1846

C. Gore Sketches of Eng. Character (1852) 78: The gossip of one fashionable dinner-table alone, within ear-shot of three or four first-rate Thomases, is sufficient to disperse throughout the town rumours enough to set a hundred families of consideration into a ferment .