Explanation

"I worked morning till noon."

"Till" is a preposition because it shows the relationship between "morning" and "noon" (expressing time).

Noun – "Till" is not a person, place, or thing.

Conjunction – "Till" can sometimes be a conjunction, but here it does not connect two clauses.

Verb – "Till" can mean "to prepare land for farming," but not in this context.

Adverb – It does not modify a verb, adjective, or another adverb.