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
see also:
far for- pardon par per annum per cent 
per centum percent per diem 

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

per diem
     adv : one every day; "we'll save 100 man-hours per diem" syn: by
           the day
see also:
by the day