fret 1 
(frĕt)
(frĕt)v. fret·ted, fret·ting, frets
v.intr.
1. To be vexed or troubled; worry. See Synonyms at brood.
2. To be worn or eaten away; become corroded.
3. To move agitatedly.
4. To gnaw with the teeth in the manner of a rodent.
v.tr.
1. To cause to be uneasy; vex: "fret thy soul with crosses and with cares" (Edmund Spenser).
2.
a. To gnaw or wear away; erode.
b. To produce a hole or worn spot in; corrode.
3. To form (a passage or channel) by erosion.
4. To disturb the surface of (water or a stream); agitate.
n.
1. The act or an instance of fretting.
2. A hole or worn spot made by abrasion or erosion.
3. Irritation of mind; agitation.
[Middle English freten, from Old English fretan, to devour; see ed- in the Appendix of Indo-European roots.]