• (RP) IPA: /ˈfað(ə)m/
• (America) IPA: /ˈfæðəm/
• (dialectal, obsolete) IPA: /ˈfædəm/

From Middle English fathome, fadom, fadme [and other forms], from Old English fæþm, fæþme [and other forms], from Proto-West Germanic *faþm, from Proto-Germanic *faþmaz, from Proto-Indo-European *pet-, *peth₂-.

• Ancient Greek πέταλος, πετᾰ́ννῡμῐ (whence English petal)
• Gothic 𐍆𐌰𐌸𐌰
• Latin pateō
• Low German fadem, faem
• Middle Dutch vadem (modern Dutch vaam, vadem)
• Norwegian Bokmål favn
• ofs fethm
• Old High German fadam, fadum (Middle High German vade, vadem, vaden, modern German Faden)
• Old Norse faþmr (Danish favn, Icelandic faðmur, Swedish famn)
• owl etem

fathom (plural fathoms)

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.
   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC ↗, Acts 27:27–28 ↗, column 2:

     [T]he ſhipmen deemed that they drew neere to ſome countrey: And ſounded, and found it twentie fathoms: and when they had gone a little further, they ſounded againe, and found it fifteene fathoms.

   • 1610–1611 (date written), William Shakespeare, “The Tempest”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC ↗, [Act I, scene i], page 5 ↗, column 1:

     Full fadom fiue thy Father lies,
     Of his bones are Corrall made:
     Those are pearles that were his eies,
     Nothing of him that doth fade,
     But doth suffer a Sea-change
     Into someting rich, & strange

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.

3. (figuratively)
   1. (chiefly, in the plural) An unspecified depth.
   2. (archaic or obsolete) Depth of insight; mental reach or scope.
      • c. 1603–1604 (date written), William Shakespeare, The Tragœdy of Othello, the Moore of Venice. […] (First Quarto), London: […] N[icholas] O[kes] for Thomas Walkley, […], published 1622, →OCLC ↗, [Act I, scene i]:

        Another of his fathome they haue not / To leade their buſineſſe, […]

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.
      • 1601 (first performance), Thomas Dekker, Satiro-mastix. Or The Untrussing of the Humorous Poet. […], London: […] [Edward Allde] for Edward White, […], published 1602, →OCLC ↗, signature E, verso ↗:

        Thy Bride, thy choice, thy vvife, / She that is novv thy fadom, […] Kneele at thy feete, obay in euerie thing, / So euerie Father is a priuate King.

   3. (figuratively) Control, grasp.
      • 1604 (first performance), [Thomas Middleton], “Inductio”, in Michaelmas Terme. […], London: […] [Thomas Purfoot and Edward Allde] for A[rthur] I[ohnson] […], published 1607, →OCLC ↗, signature A2, recto ↗:

        So; novv knovv I vvhere I am, me thinkes already / I graſpe beſt part of the Autumnian bleſſing / In my contentious fadome, […]

      • 1622 May 24 (licensing date), John Fletcher, Philip Massinger, “The Prophetesse”, in Comedies and Tragedies […], London: […] Humphrey Robinson, […], and for Humphrey Moseley […], published 1647, →OCLC ↗, Act II, scene i, page 29 ↗:

        Yes: / you have blovvne his ſvvolne pride to that vaſtnes, / as he beleeves the earth is in his fadom, / this makes him qute forget his humble Being: […]

• (unit of length) stade; toise (some contexts); brace (some contexts); braza, estadio (Spanish contexts); orguia (Greek contexts)

• French: brasse, toise
• German: Faden, Klafter
• Italian: braccio
• Portuguese: braça
• Russian: фадом
• Spanish: braza

From Middle English fathmen, fadmen [and other forms], from Old English fæðmian, from Proto-Germanic *faþmōjan, from *faþm: see further at etymology 1.

• Old High German fademōn
• Old Norse faþma (Danish favne, Icelandic faðma, Swedish famna)

fathom (fathoms, present participle fathoming; simple past and past participle fathomed)

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.

      Synonyms: figure out, puzzle out, work out

      Coordinate term: grok

      I can’t for the life of me fathom what this means.

   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.

• French: comprendre, saisir, s'imaginer
• German: ausloten, loten, sondieren
• Portuguese: sondar
• Russian: делать промер лотом
• Spanish: sondar, sondear

• German: umarmen
• Russian: обхватить
• Spanish: abrazar

• French: comprendre, saisir
• German: begreifen, ergründen, verstehen
• Italian: capire, comprendere
• Portuguese: compreender
• Russian: иссле́довать
• Spanish: ahondar, comprender, profundizar