tent peg, n.¹ — Green’s Dictionary of Slang

tent peg n.¹

[the shape, but note the Biblical story of Jael and Sisera, i.e. the penis as a weapon (cf. axe n. (2))]

the penis.

1890–1904		Farmer & Henley Sl. and Its Analogues.
1896		Farmer Vocabula Amatoria (1966) 101: Échalas, m. The penis; ‘the tent-peg.’.