I. ˈfa-thəm noun
Etymology: Middle English fadme, from Old English fæthm outstretched arms, length of the outstretched arms; akin to Old Norse fathmr fathom, Latin patēre to be open, pandere to spread out, Greek petannynai
Date: before 12th century
1. : a unit of length equal to six feet (1.83 meters) used especially for measuring the depth of water — sometimes used in the singular when qualified by a number
five fathom deep
2. : comprehension
II. verb
Date: 1607
intransitive verb
1. : probe
2. : to take soundings
transitive verb
1. : to measure by a sounding line
2. : to penetrate and come to understand
couldn't fathom the problem
• fath·om·able ˈfa-thə-mə-bəl adjective