From The Collaborative International Dictionary of English v.0.48:
Per- \Per-\ [See Per.]
1. A prefix used to signify through, throughout, by, for, or
as an intensive as perhaps, by hap or chance; perennial,
that lasts throughout the year; perforce, through or by
force; perfoliate, perforate; perspicuous, evident
throughout or very evident; perplex, literally, to
entangle very much.
[1913 Webster]
2. (Chem.) Originally, denoting that the element to the name
of which it is prefixed in the respective compounds
exercised its highest valence; now, only that the element
has a higher valence than in other similar compounds;
thus, barium peroxide is the highest oxide of barium;
while nitrogen and manganese peroxides, so-called, are not
the highest oxides of those elements.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
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]