fer·rule /ˈfɛrəl, -ul/ noun, verb, -ruled, -rul·ing.

1. a ring or cap, usually of metal, put around the end of a post, cane, or the like, to prevent splitting.
2. a short metal sleeve for strengthening a tool handle at the end holding the tool.
3. a bushing or adapter holding the end of a tube and inserted into a hole in a plate in order to make a tight fit, used in boilers, condensers, etc.
4. a short ring for reinforcing or decreasing the interior diameter of the end of a tube.
5. a short plumbing fitting, covered at its outer end and caulked or otherwise fixed to a branch from a pipe so that it can be removed to give access to the interior of the pipe.
6. Angling .
a. either of two fittings on the end of a section of a sectional fishing rod, one fitting serving as a plug and the other as a socket for fastening the sections together.
b. one of two or more small rings spaced along the top of a casting rod to hold and guide the line.

–verb (used with object)
7. to furnish with a ferrule.

Also, ferule.

1605–15; alter. (appar. conformed to L ferrum iron, -ule) of verrel, verril, late ME virole < MF (c. ML virola ) < L viriola, equiv. to viri ( a ) bracelet + –ola -ole

Source: Dictionary.com.

He brushed his gloved hands across the pommels of his daggers, the weapons slung on baldrics beneath his arms. Ever reassuring, those twin blades of Daru steel with their ferules filled with the thick, pasty poison of Moranth tralb.

Source: Toll the Hounds by Steven Erikson.