Green’s Dictionary of Slang

(UK Und.) a piece of human excrement.

c.1535		R. Copland Hye way to the Spyttel House Eiii: Cyarum by salmon and thou shalt pek my iere / In thy gan for my watch it is nace gere.
c.1566		Harman Caveat for Common Cursetours in Viles & Furnivall (1907) 86: Gerry gan, the ruffian clye thee.
1608		Dekker Lanthorne and Candle-Light Ch. 1: [as cit. c.1535] .
1610		Rowlands Martin Mark-all 39: Iere a Turd. [Ibid.] 43: If treyning thou dost feare, thou ner will foist a Ian, / Then mills and wap and treine for me, / A gere peck in thy gan.