tills

Etymology
Contraction of. Equivalent to.

Conjunction

 * 1) until (up to the time that)

Preposition

 * 1)  until (up to a certain time)

Usage notes

 * The prepositional usage of tills is sometimes proscribed in favour of given its etymology as a contraction of  which cannot be used as a preposition, but as the etymology is not clear to everyone, both usages are generally accepted.