a unit for measuring the depth of water, equal to 6 feet or 1.8 metres The ship sank in 20 fathoms. (figurative) She kept her feelings hidden fathoms deep. Word Origin Old English fæthm, of Germanic origin; related to Dutch vadem, vaam and German Faden
‘six feet’. The original sense was ‘something which embraces’, (plural) ‘the outstretched arms’; hence, a unit of measurement based on the span of the outstretched arms, later standardized to six feet.