Definitions of head-on:

• adjective:   characterized by direct opposition

  Example: "A head-on confrontation"

• adjective:   meeting front to front

  Example: "A head-on collision"

• adverb:   with the front foremost

  Example: "The cars collided head-on"

• adverb:   in direct opposition; directly

  Example: "We must meet the problem head-on"