fathom

The story

1. Proto-Indo-European · derived from*pet-
2. Proto-Germanic · inherited from*faþmaz“outstretched arms, embrace; fathom (unit of measurement)”
3. Proto-West Germanic · inherited from*faþm“outstretched arms, embrace; fathom (unit of measurement)”
4. Old English · inherited fromfæþm
5. Middle English · inherited fromfathome
6. English todayfathom

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 (petắnnūmĭ, “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”)