PM

(electromagnetism) permanent magnet
(communications) phase modulation

abbr. Provost Marshal.

See the Introduction, Abbreviations and Pronunciation for further details.

[Etymology: post meridian, i.e. after meridian] time Indicative of a time after noon, i.e. after the Sun has nominally crossed the meridian, so the time is after the meridian. Thus 12:30 p.m. identifies the moment 30 minutes after noon. Similarly 12:30 a.m. identifies the moment 30 minutes after midnight. Technically 12:00 can be neither a.m. nor p.m.; it should be qualified as midnight else as noon, when the number can be just 12. (The 24-hour clock avoids all qualification, whether by a.m. else p.m., or by noon else midnight. Its ambivalence is whether to have midnight as 24:00 in the day it ends, else 00:00 in the day it initiates; the latter is preferable.) See Universal Time re leap seconds delaying midnight.