unintentional, mistaken, accidental
incorrect
incomplete, unfinished
unpleasant
poorly, deficiently
not
unhealthy, harmful
evil
In verbs: denoting the sense "thoroughly", as in perfect.
In verbs: denoting the sense "through", as in perforate.
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.
Denoting the sense "by" or "per", as in perchance or perhaps.
Added to the name of an element in a polyatomic ion to denote the number of atoms of that element (usually four).