Green’s Dictionary of Slang

1. a nearly inaudible whisper, a grunt.

1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 135: ‘Pig’s whisper;’ is briefness itself, ’tis a grunt. What would you have of a pig but a grunt?
1831		Navy at Home I 43: [They] began to scrutinise the newcomer, whose ‘rig,’ as they termed it, in a sort of ‘pig’s whisper,’ was a ‘rum one’.
1839		Drogheda Conservative Jrnl 9 Feb. 4/2: Sis I, to the Squire in a pig’s whisper — ‘but I’m fairly done over, you must excuse me Squire, jewel, for goin’ off’.
1843		Wexford Conservative 1 Nov. 1/5: Anyone that speaks of repeal in a tone above a pig’s whisper is no friend of Ireland.
1848		Flash Dict. in Sinks of London Laid Open.
1858		Wheeling Dly Intelligencer (VA) 18 Jan. 2/1: A myriad of hungry tigers and scared dogs would have been nowhere beside it than a ‘pig’s whisper’ to the storming of Sebastopol.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1873		Sl. Dict.
1883		Dly Cairo Bulletin (IL) 21 Mar. 2/3: ‘I tuk good care av him miss,’ observed that worthy, in a tone known as a pig’s whisper.

2. a very short space of time.

1823		Rambler’s Mag. 1 Mar. 132: ‘I’ll kick the bucket in a pig’s whispher’ [sic].
1838		‘Alfred Crowquill’ Seymour’s Humourous Sketches (1866) 52: Let me have a slap at ’em [i.e. game birds] for you, and see if I don’t finish some on ’em in the twinkling of a pig's visper.
1857		Cambridge Examination Paper in C.S. Calverley Works (1901) 118: ‘Pig’s whisper’ is slang for a very brief space of time. [...] the Americans have ‘pig’s whistle’ with the same meaning.
1859		G.A. Sala Twice Round the Clock 120: An operation [i.e. accepting a bill] in comparison to the celerity of which a pig’s whisper is an age.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn) 190: Pig’s whisper [...] also a short space of time, synonymous with COCKSTRIDE, i.e., cock’s tread.
1873		Sl. Dict.
1997		Share Slanguage.