Green’s Dictionary of Slang

1. one who can be sponged on or is good for a loan [pross v.¹ (1)].

1850		Fast Man 7:1 n.p.: Mr. Widdicombe [...] had got a pros, and was gone down to Watchorns, where he was going to try to whisper him of a trifle.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor III 135/2: One will chuck you 6d., some 1s. and 2s. 6d. We call those parties ‘prosses’. [Ibid.] 139/2: ‘Is his nabs a bona pross?’ – Is he good for something to drink?

2. (also pros) a sponger, a cadger; thus, sponging [abbr. prosser n. (1)].

1846		Swell’s Night Guide 64: He’d scrap, dance, chant a square’um to his pals / No pross, nor sponge.
a.1889		‘Catnach Broadside’ n.p.: There is a josser’s land, / Far, far away! / Where a drink they never stand, / Far, far away ! Termed Prosser’s Avenue, / Where of Pros’ you meet a few. Hundreds could much better do, / Far, far away! Faraway! Faraway! [B&L].

3. a prostitute’s client.

1846

Swell’s Night Guide 36: Many of the finest of the Oxford-street birds flutter in here [...] nightbirds, but very few green ones among them. They are certainly a mere mercenary lot, and can go in on a pross rumbo.

4. see pros n. (1)