On

spatial preposition

often translated by "sur"

• In X is on Y there is contact on at least one side, if Y disappeared, X would fall or disappear.
• Dans la phrase X is on Y, il y a contact d'un côté. Si Y disparassait, X tomberait ou disparaitrait.
  • The book is on the desk.
  • The ornaments are on the tree.
  • The writing is on the wall.

particle

Sometimes translatable with "à"

pre-established circuit marker, with off as its antonym. transmission of energy (turn SO on / turn SO off).

turn on/off

get on/off the bus

on schedule, on time

on the clock, online, on the phone, on TV, on camera, on the air, etc.

turn SO on (Cf. Nora Jones), lead on, get on (a project)

Continuative particle

Move on, lead on, carry on, get on (in age)

evolution

introduced -ing nominals (historically)

On Hunting --> a-hunting --> hunting.

Combined with other prepositions

on (the condition) less than --> unless

on till --> until

on --> a (ahead, above, afore, etc.)