Looking for etymology of thimble, I found this:
Thumb: (Old English) The thumb is etymologically the 'swollen' part -
an allusion to its greater thickness than the other fingers. Along with
its relatives German daumen and Dutch duim, it goes back to a
prehistoric West Germanic thûmon. This in turn can be traced to
Indo-European tum- 'swell', which also produced English tumour, and
tumult. The b in thumb appeared in the early Middle English period,
when it was still a two syllable word (thumbe), and at first was
pronounced, but it has fallen silent over the centuries. The words
thigh and thimble have related origins.

In site of nautical terms, I found this:
THIMBLE. An iron ring, having a groove formed in its outer circumference. Thimbles are fixed on the cringles of sails where iron hooks are used, as the hook of a tackle, &c.