Definitions of first:

• noun:   an honours degree of the highest class
• noun:   the first element in a countable series

  Example: "The first of the month"

• noun:   the first or highest in an ordering or series

  Example: "He wanted to be the first"

• noun:   the fielding position of the player on a baseball team who is stationed at first base
• noun:   the lowest forward gear ratio in the gear box of a motor vehicle; used to start a car moving
• noun:   the time at which something is supposed to begin
• adjective:   indicating the beginning unit in a series
• adjective:   being the gear producing the lowest drive speed

  Example: "Use first gear on steep hills"

• adjective:   ranking above all others

  Example: "Was first in her class"

• adjective:   preceding all others in time or space or degree

  Example: "The first house on the right"

• adjective:   highest in pitch or chief among parts or voices or instruments or orchestra sections

  Example: "First soprano"

• adjective:   serving to begin

  Example: "The first verse"

• adjective:   serving to set in motion

  Example: "His first (or maiden) speech in Congress"

• adverb:   before anything else

  Example: "First we must consider the garter snake"

• adverb:   the initial time

  Example: "When Felix first saw a garter snake"

• adverb:   before another in time, space, or importance

  Example: "I was here first"

• adverb:   prominently forward
• name:  A surname (very rare: popularity rank in the U.S.: #29015)