Etymology
Advertisement
on- 

the preposition and adverb on used as a prefix; Old English on-, an-.

Related entries & more 
Advertisement
-on 
subatomic particle suffix, from ion.
Related entries & more 
on (prep., adv.)

"in a position above and in contact with; in such a position as to be supported by;" also noting the goal to which some action is or has been directed; "about, concerning, regarding; in a position to cover;" as an adverb, "in or into a position in contact with and supported by the top or upper part of something; in or into place; in place for use or action; into movement or action; in operation," Old English on, unstressed variant of an "in, on, into," from Proto-Germanic *ana "on" (source also of Dutch aan, German an, Gothic ana "on, upon"), from PIE root *an- (1) "on" (source also of Avestan ana "on," Greek ana "on, upon," Latin an-, Old Church Slavonic na, Lithuanian nuo "down from").

Also used in Old English in many places where we now would use in. From 16c.-18c. (and still in northern England dialect) often reduced to o'. Phrase on to "aware" is from 1877.

Related entries & more 
clip-on (adj.)

"held on by means of a clip," 1909, from the verbal phrase; see clip (v.2) + on (adv.).

Related entries & more 
hang on (v.)
1860, "to remain clinging," 1860, especially "cling fondly to" (1871); see hang (v.) + on (adv.). As a command to be patient, wait a minute, from 1936, originally in telephone conversations.
Related entries & more 
Advertisement
hard-on (n.)
"penile erection," 1922, earlier as an adjective (1893), from hard + on.
Related entries & more 
add-on (n.)
"additional component," 1941, from verbal phrase add on; see add (v.) + on (adv.).
Related entries & more 
walk-on (n.)
"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.
Related entries & more 
on-site (adj.)
also onsite, 1959, from on + site. Originally in reference to Cold War military inspections.
Related entries & more