Ahead
Part of speech: adverb
Definition: In or to the front; in advance; onward.
Example sentence: We can only see a short distance ahead, but we can see plenty there that needs to be done.
Beforehand
Part of speech: adverb
Definition: At an earlier or preceding time.
Example sentence: It is only by risking our persons from one hour to another that we live at all. And often enough our faith beforehand in an uncertified result is the only thing that makes the result come true.