Green’s Dictionary of Slang

the afternoon; also attrib.

1862		‘Artemus Ward’ Artemus Ward, His Book 130: I arroved in Cleveland on Saturday P. M. from Baldinsville jest in time to fix myself up.
1906		Sun. Times (Perth) 11 Mar. 4/7: This p.m. [...] had a long black strip of cloud, like a streak of dirt on a child’s face, that came between the sun and the edge of the earth.
1922		R. Lardner ‘A Caddy’s Diary’ in Coll. Short Stories (1941) 396: I heard him say he got a 88 in the p.m. which is about a 94 but anyway it was good enough to win.
1933		E.C. Segar ‘Thimble Theatre’ [comic strip] We’ll sail this p.m. if possible.
1939		W. Winchell ‘On Broadway’ 8 Jan. [synd. col.] The primrose pathologists split their diagnoses, the ayem boys giving it ‘No sir’ and most of the peeyem lads agreeing [...] that it was ‘grand.’.
1942		‘Marienne’ ‘Solid Meddlin’’ in People’s Voice (NY) 14 Mar. 33/1: [B]attle of music between Charlie Barnett and Erskine Hawkins [...] on the same p-yem.
1946		J. Evans Halo in Blood (1988) 148: I came out to see him earlier this p.m.
1990		S. Morgan Homeboy 266: These mainline ayems and peeyems got me doubleparked in the Twilight Zone.
2009		L. McIlvanney All the Colours 16: [T]he back nine at Eaglesham, or a stool in the Cope, or wherever they went on a Tuesday pm.