Cases of word usage

1) that part of a horse's harness that goes on its head, including the metal bit for the mouth, the straps and the rains (bridle)

2) a person more interested in what goes on around her or him than in personal thoughts and feelings (extrovert)

3) a person who goes into an unexplored or undeveloped country to settle or work there; the first person to begin a new branch of study, method etc (pioneer)

4) a section of a road that goes under another road or railway (underpass)