Synonyms for Per diem:

adj.

daily (adjective)
daily, quotidian, diurnal.

n.

expense, Overpaid, low-paid, overpay, earnings-related, paid, outlay, hourly, net, gross, pay. per day (noun)
by the day, daily.
per diem (noun)
by the day.

Other synonyms:

Overpaid, low-paid, earnings-related. overpay. hourly, paid. pay. Other relevant words:
by the day.