"penile erection," 1922, earlier as an adjective (1893), from hard + on.

"additional component," 1941, from verbal phrase add on; see add (v.) + on (adv.).

"minor non-speaking role," 1902, theatrical slang, from the verbal phrase walk on, attested in theater jargon by 1897 with a sense "appear in crowd scenes," from walk (v.) + on (adv.). Meaning "actor who has such a part" is attested from 1946. The sports team sense is recorded from 1974.

also onsite, 1959, from on + site. Originally in reference to Cold War military inspections.

"ruse, deception," 1937, from earlier adjectival meaning "assumed, feigned" (1620s), a figurative extension of the verbal phrase on the notion of putting on costumes or disguises. To put on (v.), of clothes, garments, etc., is by early 15c.; see from put (v.) + on (adv.). Hence "clothe, cover, assume as covering" (mid-15c.) and "assume the garb or appearance of" (real or feigned), 1520s. The expression put (someone) on "play a trick on, deceive" (by 1958) seems to be a back-formation from the noun.

1640s, "continue to advance," also "manage, be engaged in," from carry (v.) + on (adv.). The meaning "conduct oneself in a wild and thoughtless manner" is by 1828. Carryings-on is from 1660s as "questionable doings," from 1866 as "riotous behavior." As an adjective, carry-on, in reference to luggage that may be brought into the passenger compartment of an airliner, is attested by 1965.

1959, from the verbal phrase, from iron (v.) + on (adv.).

that which arouses or excites, 1968, originally of psychedelic drugs, from verbal phrase turn on "activate (a mechanism)" (1833), specifically from figurative sense turn (someone) on "excite, stimulate, arouse," recorded from 1903; from turn (v.) + on (adv.).

1590s, "to put on," from get (v.) + on (adv.). Meaning "prosper" is from 1785; that of "to advance, make progress" is from 1798; that of "be friendly" (with) is attested by 1816.

by 1969, originally in reference to the use of computers in education; see hand (n.) + on (adv.).