from The American Heritage® Dictionary of the English Language, 4th Edition
- Thoroughly; completely; intensely: perfervid.
- Containing an element in its highest oxidation state: perchloric acid.
- Containing a large or the largest possible proportion of an element: peroxide.
- Containing the peroxy group: peracid.
- Slang Very: percool, as in "That shirt is percool, man!”
from Wiktionary, Creative Commons Attribution/Share-Alike License
- Denoting the sense "by" or "per", as in perchance or perhaps.
- In verbs: denoting the sense "through", as in perforate.
- In verbs: denoting the sense "thoroughly", as in perfect.
- In verbs: denoting the sense "to destruction", as in pervert.
- In adjectives and adverbs: denoting the sense "extremely", as in perfervid.
- Forming nouns and adjectives denoting the maximum proportion of one element in a compound, as in peroxide.
- Added to the name of an element in a polyatomic ion denote the number of that element (usually four).
from the GNU version of the Collaborative International Dictionary of English
- 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.
- 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.
Latin, from per, through; see per1 in Indo-European roots.(American Heritage® Dictionary of the English Language, Fourth Edition)
From Old French per (modern French par) (Wiktionary)
From Latin per- (Wiktionary)