I. per di‧em¹ /pə ˈdiːəm $ pər-/ noun [countable] American English

1. an amount of money that an employer pays a worker for each day that is worked

2. an amount of money that a worker is allowed to spend when doing his or her job, for example on a business trip:
a per diem allowance

[TahlilGaran] Dictionary of Contemporary English ▲

II. per diem² adverb American English formal
[Date: 1500-1600; Language: Latin; Origin: 'by the day']
for each day or on each day:
workers who are paid per diem

[TahlilGaran] Dictionary of Contemporary English ▲