Per is defined as to, for, by or according to.(preposition)
An example of per used as a preposition is in the phrase, "as per standards," which means by the standards.
Per mean for each once.(adverb)
An example of per used as an adverb is in the phrase, "one cookie per person," which means one cookie for each person.
See per in Webster's New World College Dictionary
Origin: L < IE base *per-, a going beyond > far, for
Origin: L < per, through: see per
See per in American Heritage Dictionary 4
Origin: Latin; see per1 in Indo-European roots.
Origin: , from per, through; see per1 in Indo-European roots.
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