ruck 2 
(rŭk)
(rŭk)v. rucked, ruck·ing, rucks
v.tr.
To make a fold in; crease.
v.intr.
To become creased.
n.
A crease or pucker, as in cloth.
[Ultimately from Old Norse hrukka, wrinkle, fold; see sker-2 in the Appendix of Indo-European roots.]