Longman Dictionary of Contemporary English
The Collaborative International Dictionary
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.
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.
Per annum, by the year; in each successive year; annually.
Per cent, Per centum, by the hundred; in the hundred; -- used esp. of proportions of ingredients, rate or amount of interest, and the like; commonly used in the shortened form per cent.
Per diem, by the day. [For other phrases from the Latin, see Quotations, Phrases, etc., from Foreign Languages, in the Supplement.]
Douglas Harper's Etymology Dictionary
Wiktionary
a. per day, daily n. 1 a daily stipend 2 a daily allowable limit for expendables
WordNet
adv. one every day; "we'll save 100 man-hours per diem" [syn: by the day]
Wikipedia
Per diem ( Latin for "per day" or "for each day") is a daily allowance for expenses—a specific amount of money an organization gives an individual, often an employee, per day to cover living expenses when traveling for work.
A per diem can include part or all of the expenses incurred, for example it may exclude accommodation (for which reimbursement may be available on presentation of receipts) and only cover meals. Per diem is also used as an adjective and an adverb. Travel, particularly by motor vehicles, is often reimbursed at a rate determined only by distance travelled, e.g., the US Business Mileage Reimbursement Rate.
Fixed per diem (and per mile) rates eliminate the need for employees to prepare, and employers to scrutinise, a detailed expense report with supporting receipts to document amounts spent while travelling on business. Instead, employers pay employees a standard daily rate without regard to actual expenditure.
Usage examples of "per diem".
So Colonel Rachner Thract, formerly of the unnamed service, found himself with a salary and per diem worthy of full duty.
A per diem you receive as a supplement to your salary regardless of how you spend it.
I lower my per diem and instead take some points on the net, if and when.
I won't take more than five points at most, and I won't do a held survey for less than expenses plus a per diem of fifteen dollars a day, minimum.
My dear, there are plenty of lawyers who get paid that much per diem for nice clean work in a warm courtroom.
That there shall be paid for each waggon, with four good horses and a driver, fifteen shillings per diem.
I couldn't afford it, so I took most of my meals from the Corporation's refectories, included in the price of my per-capita per diem.
Then too, he ate inexpensive snacks for lunch and dinner so he could pocket the per diem allowance the FBI paid for food.