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.

Definitions of on
on (adv.)
with a forward motion;
march on
the circus traveled on to the next city
Synonyms: along
on (adv.)
indicates continuity or persistence or concentration;
shall I read on?
his spirit lives on
on (adv.)
in a state required for something to function or be effective;
turn the lights on
get a load on
on (adj.)
in operation or operational;
left the oven on
on (adj.)
(of events) planned or scheduled;
we have nothing on for Friday night
the picnic is on, rain or shine