On

particle

Marks a pre-established circuit, and has 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 on (Cf. Nora Jones), lead on

Continuative particle

Move on, lead on, carry on

evolution

On Hunting --> a-hunting --> hunting. on (the condition) less than --> unless

on till --> until