grommet

n. [ F. gourmette curb, curb chain, fr. gourmer to curb, thump, beat; cf. Armor. gromm a curb, gromma to curb. ] 1. A ring formed by twisting on itself a single strand of an unlaid rope. Sometimes written grummet. [ 1913 Webster ]

2. Any eyelet or ring of metal or other material inserted in a hole in a sheet of some other material; in sailing, a metallic ring in or for a sail or a mailbag. [ 1913 Webster ]

3. A ring of rubber or other insulating material inserted in a hole in some surface of a device, to prevent wires passing through the hole from making contact with the surface; used especially in electrical and electronic devices, to prevent undesired electrical contact. [ PJC ]

4. (Mil.) A ring of rope used as a wad to hold a cannon ball in place. [ 1913 Webster ]