Dimeback

In American football, a dimeback is a cornerback or safety who serves as the sixth defensive back (fourth cornerback or third safety) on defense. The third cornerback on defense is known as a nickelback. The dimeback position is essentially relegated to backup cornerbacks and safeties who do not play starting cornerback or safety positions. Dimebacks are usually fast players because they must be able to keep up on passing plays with 3+ wide receivers.