Before
Part of speech: preposition
Definition: Earlier than (in time). In front of in space. Under consideration, judgment, authority of (someone) In store for, in the future of (someone). In front of, according to a formal system of ordering items. At a higher or greater position in a subjective ranking
Part of speech: adverb
Definition: at an earlier time in advance
Part of speech: conjunction
Definition: in advance of the time when rather or sooner than
Example sentence: The woods are lovely, dark and deep. But I have promises to keep, and miles to go before I sleep.
Ahead
Part of speech: adverb
Definition: In or to the front; in advance; onward.
Example sentence: It isn't the mountains ahead to climb that wear you out; it's the pebble in your shoe.