'Per diem' definitions:

Definition of 'per diem'

adverb

One every day; "we'll save 100 man-hours per diem" [syn: per diem, by the day]

noun

A daily allowance for living expenses (especially while traveling in connection with your job)

From: GCIDE

Per \Per\, prep. [L. Cf. Far, For-, Pardon, and cf. Par, prep.] Through; by means of; through the agency of; by; for; for each; as, per annum; per capita, by heads, or according to individuals; per curiam, by the court; per se, by itself, of itself. Per is also sometimes used with English words. [1913 Webster]
Per annum, by the year; in each successive year; annually.
per cent, Per centum, percent, by the hundred; in the hundred; a proportion multiplied by one hundred; -- used esp. of proportions of ingredients, rate or amount of interest, and the like; most commonly used in the shortened form per cent; as, 5 is ten per cent of 50. It is commonly symbolized with the per cent sign, "%".
Per diem, by the day. [For other phrases from the Latin, see Quotations, Phrases, etc., from Foreign Languages, in the Supplement.] [1913 Webster]

From: GCIDE

Per diem \Per di"em\ [L.] By the day; substantively (chiefly U. S.), an allowance or amount of so much by the day. Also used adjectivally; as, a per diem allowance. [Webster 1913 Suppl. +PJC]