Frock
late Middle English: from Old French froc, of Germanic origin. The sense ‘priest's or monk's gown’ is preserved in defrock .
wiktionary
From Middle English frok, frokke, from Old French froc(“frock, a monk's gown or habit”), perhaps via Medieval Latin hrocus, roccus, rocus(“a coat”), from Frankish *hroc, *hrok(“skirt, dress, robe”), from Proto-Germanic *hrukkaz(“robe, jacket, skirt, tunic”), from Proto-Indo-European *kreḱ-(“to weave”). Cognate with Old High German hroch, roch(“skirt, dress, cowl”) – whence German Rock(“skirt, coat”) –, Saterland Frisian Rok(“skirt”), Dutch rok(“skirt, petticoat”), Old English rocc(“an overgarment, tunic, rochet”), Old Norse rokkr(“skirt, jacket”), whence Danish rok(“garment”).
From Middle English froke, variation of frogge(“frog”), from Old English frocga(“frog”). More at frog.
etymonline
frock (n.)
mid-14c., from Old French froc "a monk's habit; clothing, dress" (12c.), which is of unknown origin; perhaps from Frankish *hrok or some other Germanic source (compare Old High German hroc "mantle, coat;" Old Norse rokkr, Old English rocc, Old Frisian rokk, German Rock "a coat, over-garment"). Another theory traces it to an alteration of Medieval Latin floccus, from Latin floccus "tuft of wool," a word of unknown origin. Meaning "outer garment for women or children" is from 1530s. Frock-coat attested by 1819.
