per

American Heritage® Dictionary of the English Language, Fourth Edition

1. prep. To, for, or by each; for every: Gasoline once cost 40 cents per gallon.
2. prep. According to; by: Changes were made to the manuscript per the author's instructions.
3. prep. By means of; through.
4. adv. Informal For each one; apiece: sold the cookies for one dollar per.
5. adv. Informal Per hour: was driving at 60 miles per.

Century Dictionary and Cyclopedia

1. Through; by means of. A Latin preposition, the source of the prefix per-, and used independently in certain Latin phrases common in English use, as per se, per saltum, especially in law phrases, as per capita, per curiam, per pares, per stirpes, etc. and certain common commercial phrases, as per centum, per diem, per annum, whence, by an imperfect translation, as a quasi-English preposition, in similar commercial phrases with an English noun, as per day, per week, per year, per hour, per hundred, per dozen, etc., per bearer, per express, by credit as per ledger, received per steamer Southampton, etc.
2. A prefix of Latin origin, meaning primarily ‘through.’ See the etymology. It occurs chiefly in words formed in Latin, as in peract, peragrate, perambulate, etc. Though the primary sense of per- is usually distinctly felt in English, it is scarcely used in the formation of new words.
3. As an inseparable prefix of intensity, ‘thoroughly,’ ‘very,’ as in peracute, perfervid, pellucid; specifically, in chem., noting the maximum or an unusual amount, as peroxid, the highest oxid, or an oxid containing more oxygen than the protoxid, etc.
4. n. In petrography, in the quantitative system of classification of igneous rocks (see rock), a prefix used to form adjectives, and showing that the factor or component indicated is present in any division of igneous rocks, alone or in extreme amount — that is, that its ratio to another factor is greater than : as, peralkalic, perfelic, perfemane, perfemic, etc.
5. n. An abbreviation of period.

Wiktionary

1. prep. for each
2. prep. to each, in each (used in expressing ratios of units)
3. prep. medicine via (the), by (the), through (the) (followed by Latin name for an orifice)
4. prep. in accordance with
5. pro. neologism they (singular). Gender-neutral third-person singular subject pronoun, coordinate with gendered pronouns he and she.
6. pro. neologism them (singular) Gender-neutral third-person singular object pronoun, grammatically equivalent to the gendered him and her.
7. adj. neologism Belonging to per, their (singular). Gender-neutral third-person singular possessive adjective, coordinate with gendered his and her.

GNU Webster's 1913

1. prep. Through; by means of; through the agency of; by; for; for each. Per is also sometimes used with English words.