on
Definition of on:
part of speech: pronoun
part of speech: adverb
Forward in progression; in continuance; without ceasing; opposed to off; on a sudden, suddenly.
part of speech: preposition
Above, and in contact with the upper surface of a thing; not off; upon; at or near; denoting dependence or reliance; denoting nearness or closeness; denoting addition or accumulation.
part of speech: interjection
A word of excitement or encouragement to attack or advance; a contraction for go on.