Merriam-Webster's Collegiate® Dictionary, 11th Edition
BEFORE
I. adverb or adjective
Etymology: Middle English, adverb & preposition, from Old English beforan, from be- + foran before, from fore Date: before 12th century in advance ; ahead , at an earlier time ; previously ,
II. preposition Date: before 12th century
1. a. forward of ; in front of , in the presence of , under the jurisdiction or consideration of , c. at the disposal of , in store for , preceding in time ; earlier than , in a higher or more important position than ,
III. conjunction
Date: 13th century
1. a. earlier than the time that , sooner or quicker than , so that…do not , until the time that , c. or else…not , or else , rather or sooner than