Per-

CIDE DICTIONARY

Per-,  [See Per.].

•  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]
•  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]

OXFORD DICTIONARY

Per-, prefix.
1 forming verbs, nouns, and adjectives meaning: a through; all over (perforate; perforation; pervade). b completely; very (perfervid; perturb). c to destruction; to the bad (pervert; perdition).
2 Chem. having the maximum of some element in combination, esp.: a in the names of binary compounds in -ide (peroxide). b in the names of oxides, acids, etc. in -ic (perchloric; permanganic). c in the names of salts of these acids (perchlorate; permanganate).

Etymology

L per- (as PER)