"by himself, herself, or itself," 1570s, Latin, literally "by itself;" from per (see per) + se (see se-). The Latin phrase translates Greek kath auto (Aristotle).

"in each year, annually," c. 1600, Latin, "by the year," from per (see per) + annum, accusative singular of annus "year" (see annual (adj.)).

1510s, "by the day, in each day," Latin, "by the day," from per (see per) + diem, accusative singular of dies "day" (from PIE root *dyeu- "to shine"). As a noun from 1809, "amount or allowance of so much every day."

1680s, Latin, "by the head, by heads," from per (see per) + capita "head" (see capital).

1680s, Latin, "by families, by stocks;" in legal use, for inheritances, etc., opposed to per capita. See per- + stirpes.

[A]pplied to succession when divided so as to give the representatives belonging to one branch the share only that their head or ancestor would have taken had he survived. Thus, in a gift to A and the children of B, if they are to take per capita, each child will have a share equal to that of A; but if they are to take per stirpes, A will take one half and the other half will be divided among the children of B. [Century Dictionary]

French, from Latin per excellentiam "by the way of excellence." French par "by, through, by way of, by means of" is from Latin per (see per). For second element, see excellence.

denoting clothes sold in standard sizes, 1957, from French prêt à porter, "ready-to-wear." For pret, see presto. Porter is literally "to carry," from Latin portare "to carry" (from PIE root *per- (2) "to lead, pass over"). For a similar sense evolution, compare German kleider tragen.