Through; all over; completely.
[Latin per, through, by means of.]
Words containing this combining form have frequently come directly from Latin or through French with the initial per- already attached; it is not an active word-forming element.
Examples in which it means ‘through’ or ‘all over’ include perforate (Latin perforare, from forare, to pierce); perambulate (Latin perambulare, from ambulare, to walk); pervade (Latin pervadere, from vadere, to go); and peroration (Latin perorat-, spoken at length, from orare, speak). It can suggest an action taken to completion, as in the verb perfect (Latin perficere, from facere, to do). It can sometimes imply destruction, as in perdition (Latin perdere, to destroy, from the base of dare, to put) or perish (Latin perire, pass away, from ire to go). Peremptory, insisting on immediate attention or obedience, originally meant decisive (Latin peremptorius, deadly, decisive, from perempt-, destroyed, cut off, from emere, to take).
In chemistry per- implies that an element is present in the maximum proportion possible, or that that the principal atom is in a higher state of oxidation than usual, as in peroxide, perchlorate, permanganate, or perborate; in this sense per- forms compound prefixes such as perchloro-, perfluoro-, and peroxy-. In modern systematic naming, specific prefixes are preferred (manganese dioxide to manganese peroxide; tetrachloroethylene to perchloroethylene, and so on), though many names in per- are preserved in popular use.