guide-post, n. — Green’s Dictionary of Slang

guide-post n.

[he is supposed to guide the congregation to heaven; despite Grose’s instruction to ‘see guide post’ there is no such entry; one is presumably meant to infer the reverse definition oneself]

a clergyman.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Parson, a guide post, hand or finger post by the road side for directing travellers, compared to a parson, because like him it sets people in the right way. See guide post.
1811		Lex. Balatronicum.
1825		‘Evry Man to His Trade’ in Universal Songster I 5/1: Said he, sir, I’d have you to know / I’m a bishop / [...] / Said I in a laugh / You’re a guide-post by gum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1895		Crowe Aus. Sl. Dict. 34: Guide Posts, ministers of the gospel.