fist 
(fĭst)
(fĭst)n.
1. The hand closed tightly with the fingers bent against the palm.
2. Informal A grasp; a clutch: had a fortune in their fists and let it go.
tr.v. fist·ed, fist·ing, fists
1. To clench into a fist.
2. To grasp with the fist.
3. Vulgar To insert the hand into the rectum or vagina of (someone) as a means of sexual stimulation.
[Middle English, from Old English fȳst; see penkwe in the Appendix of Indo-European roots.]