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fathom [fathom 词源字典]: fathom: [OE] The underlying etymological meaning of fathom appears to be ‘stretching out, spreading’. It probably comes ultimately from the Indo-European base *pot-, *pet-, which also produced Latin patēre ‘be open’ (source of English patent) and Greek pétalos ‘outspread’ (source of English petal). Its Germanic descendant was *fath-, which produced the noun *fathmaz, direct ancestor of Old English fæthm.

Here, the notion of ‘stretching out’ seems to have spread via ‘stretching out the arms’ to, on the one hand ‘embrace’ (and one meaning of Old English fæthm was ‘embrace, bosom’), and on the other ‘length spanned by outstretched arms’ – about six feet.
=> patent, petal[fathom etymology, fathom origin, 英语词源]
clip (v.2): "fasten, hold together by pressure," also (mostly archaic) "to embrace," from Old English clyppan "to embrace, clasp; surround; prize, honor, cherish;" related to Old Frisian kleppa "to embrace, love," Old High German klaftra, German klafter "fathom" (on notion of outstretched arms). Also compare Lithuanian glebys "armful," globiu "to embrace, support." Meaning "to fasten, bind" is early 14c. Meaning "to fasten with clips" is from 1902. Related: Clipped; clipping. Original sense of the verb is preserved in U.S. football clipping penalty.
fathom (n.): Old English fæðm "length of the outstretched arm" (a measure of about six feet), also "arms, grasp, embrace," and, figuratively "power," from Proto-Germanic *fathmaz "embrace" (cognates: Old Norse faðmr "embrace, bosom," Old Saxon fathmos "the outstretched arms," Dutch vadem "a measure of six feet"), from PIE *pot(ə)-mo-, from root *petə- "to spread, stretch out" (see pace (n.)). It has apparent cognates in Old Frisian fethem, German faden "thread," which OED explains by reference to "spreading out." As a unit of measure, in an early gloss it appears for Latin passus, which was about 5 feet.
outstretch (v.): mid-14c., from out + stretch (v.). Related: Outstretched; outstretching.
pace (n.): late 13c., "a step in walking; rate of motion," from Old French pas "a step, pace, trace," and directly from Latin passus, passum "a step, pace, stride," noun use of past participle of pandere "to stretch (the leg), spread out," probably from PIE *pat-no-, a nasalized variant of root *pete- "to spread" (cognates: Greek petannynai "to spread out," petalon "a leaf," patane "plate, dish;" Old Norse faðmr "embrace, bosom," Old English fæðm "embrace, bosom, fathom," Old Saxon fathmos "the outstretched arms"). Also, "a measure of five feet" [Johnson]. Pace-setter in fashion is from 1895.