work on vs till

work on is not a noun while till is a noun.

Word	Noun	Adjective	Verb	Adverb
work on	No	No	Yes	No
till	Yes	No	Yes	No

As verbs, till is a hyponym of work on; that is, till is a word with a more specific, narrower meaning than work on:

work on: shape, form, or improve a material
till: work land as by ploughing, harrowing, and manuring, in order to make it ready for cultivation

Other hyponyms of work on include hot-work, cold work, coldwork, overwork, make over, retread, rework, rack, tool.

work on (noun)	till (noun)
	a strongbox for holding cash
	a treasury for government funds
	unstratified soil deposited by a glacier; consists of sand and clay and gravel and boulders mixed together

work on (verb)	till (verb)
shape, form, or improve a material	work land as by ploughing, harrowing, and manuring, in order to make it ready for cultivation
to exert effort in order to do, make, or perform something