strop n.

1610s, "band of leather," from Scottish and/or nautical variant of strope "loop or strap on a harness" (mid-14c.), probably from Old French estrop "strap," from Latin stroppus "strap, band," perhaps via Etruscan, ultimately from Greek strophos "twisted band; a cord, rope," from strephein "to turn" (from PIE root *streb(h)- "to wind, turn"). Old English stropp, Dutch strop "halter" also are borrowed from Latin, and the Old English word might be the source of the modern one. Slang meaning "credit" is from 1828.

Proto-Indo-European root meaning "to wind, turn."

It forms all or part of: anastrophe; antistrophe; apostrophe (n.1); apostrophe (n.2); boustrophedon; catastrophe; epistrophe; strabismus; strap; strep; strepto-; streptococcus; streptomycin; strobe; strobic; stroboscope; strop; strophe; strophic.

It is the hypothetical source of/evidence for its existence is provided by: Greek strophe "stanza," originally "a turning," strephein "to turn," strophaligs "whirl, whirlwind," streblos "twisted," stremma "that which is twisted."