Green’s Dictionary of Slang

1. a hypocrite.

1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1824		Pierce Egan’s Life in London 21 Nov. 341/2: The canting hypocrisy of the ‘Saints’.

2. (US campus) a notably religious student.

1803		‘A Pembrochian’ Gradus ad Cantabrigiam 116: saints. ‘A set of men who have great pretensions to particular sanctity of manners, and zeal for orthodoxy.’.
1847		Blackwood’s Mag. LX 148: If he had been a hard-reading man from choice, — or a stupid man, — or a ‘saint,’ — no one would have troubled themselves about him.
1856		B.H. Hall College Words (rev. edn) 399: saint. A name among students for one who pretends to a particular sanctity of manners.

3. (N.Z. prison) a skillful thief.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 158/1: saint, the n. 1 Mount Eden Men’s Prison 3 an exceptionally good thief.

4. (N.Z. prison) a skillful thief.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 158/1: saint, the n. 1 Mount Eden Men’s Prison.