American Heritage Second College Edition (c)1976:

strop: n. A flexible strip of leather or canvas used for sharpening a razor. -tr.v. stropped, strop*ping, strops. To sharpen (a razor) on a strop. [ME stroppe, band of leather < MLG strop < Lat. Stoppus <Gk strophion]

Laminated on the back of a whetstone? Sounds like a pad to stop it from slipping around as opposed to something for sharpeining (or, more precisely, honing in the case of a strop). (/me ducks as Bitt goes for the Oxford Unabridged...)

One gets to use the word so infrequently; I just needed to take it out for a spin since the chance arose.

-Zeke