fathom

Etymology 1

From Middle English fathome, fadom, fadme (“unit of length of about six feet; depth of six feet for nautical soundings; (loosely) cubit; ell”) [and other forms], from Old English fæþm, fæþme (“encircling or outstretched arms, bosom, embrace; envelopment; control, grasp, power; fathom (unit of measurement); cubit”) [and other forms], from Proto-West Germanic *faþm (“outstretched arms, embrace; fathom (unit of measurement)”), from Proto-Germanic *faþmaz (“outstretched arms, embrace; fathom (unit of measurement)”), from Proto-Indo-European *pet-, *peth₂- (“to spread out; to fly”). cognates * Ancient Greek πέταλος (pétalos, “broad; flat”), πετᾰ́ννῡμῐ (petánnūmi, “to open; to spread out; to be dispersed or scattered”) (whence English petal) * Gothic 𐍆𐌰𐌸𐌰 (faþa, “fench; hedge”) * Latin pateō (“to extend, increase; to be accessible, attainable, open; to be exposed, vulnerable”) * Low German fadem, faem (“cubit; thread”) * Middle Dutch vadem (modern Dutch vaam, vadem (“fathom”)) * Norwegian Bokmål favn (“an embrace; a fathom”) * Old Frisian fethm (“outstretched arms”) * Old High German fadam, fadum (“cubit”) (Middle High German vade (“enclosure”), vadem, vaden, modern German Faden (“fathom; filament, thread”)) * Old Norse faþmr (Danish favn (“an embrace; a fathom”), Icelandic faðmur (“an embrace”), Swedish famn (“the arms, bosom; an embrace”)) * Old Welsh etem (“thread”)

noun

1. (chiefly nautical, historical, US) A man's armspan, generally reckoned to be six feet (about 1.8 metres). Later used to measure the depth of water, but now generally replaced by the metre outside American usage.
2. (nautical, US) A measure of distance to shore: the nearest point to shore at which the water depth is the value quoted.
   After we'd rowed for an hour, we found ourselves stranded ten fathoms from shore.
   At fifty fathoms, the waters of the Southern Ocean are dark blue. 1983, Richard Ellis, “The Predators”, in The Book of Sharks, 1st paperback edition, New York, N.Y.: Alfred A[braham] Knopf, published 1989, page 7
3. (figurative)
   1. (chiefly in the plural) An unspecified depth.
   2. (archaic or obsolete) Depth of insight; mental reach or scope.
4. (obsolete)
   1. The act of stretching out one's arms away from the sides of the torso so that they make a straight line perpendicular to the body.
   2. Someone or something that is embraced.
   3. (figurative) Control, grasp.

Etymology 2

From Middle English fathmen, fadmen (“to encircle (something) with the arms, embrace; to feel, grope; to measure by the ell (or perhaps the fathom)”) [and other forms], from Old English fæðmian, from Proto-Germanic *faþmōjan, from *faþm (“outstretched arms, embrace; fathom (unit of measurement)”): see further at etymology 1. cognates * Old High German fademōn * Old Norse faþma (Danish favne (“to embrace”), Icelandic to embrace, hug; to cuddle, Swedish famna)

verb

1. (transitive)
   1. (also figurative) To measure the depth of (water); to take a sounding of; to sound.
   2. (archaic or obsolete) To encircle (someone or something) with outstretched arms; specifically, to measure the circumference or (rare) length of something.
   3. (figurative) Often followed by out: to deeply understand (someone or something); to get to the bottom of.
      Coordinate term: grok
      I can’t for the life of me fathom what this means.
      Otamendi’s selection ahead of Vincent Kompany was difficult to fathom and, apart from Fernandinho, City’s line-up was otherwise filled with attacking players. 10 April 2018, Daniel Taylor, “Liverpool go through after Mohamed Salah stops Manchester City fightback”, in The Guardian (London)
   4. (obsolete) To embrace (someone or something).
2. (intransitive)
   1. To measure a depth; to sound.
   2. (figurative) To conduct an examination or inquiry; to investigate.