A small cap worn over the fingertip for protection
[DOC] [TLE] thimble - Memidex dictionary/thesaurus [PAR] Type of: containerful; (container) a small metal cap to protect the finger while 
sewing; ... a small cap, usually of metal, worn over the fingertip to protect it when
... [DOC] [TLE] thimble - ...   thimble?