Also, I'm curious if there is a reconstructed Slavic root or if it's a loan (nothing found in Derksen).
I'm not sure about exact proto-Slavic root but it's generally accepted as word of (at least) eastern-Slavic origin. And, as of Russian, yep, cognates for "кравець" are "кроить" and its derivatives, such as "крой", "закройщик".
"Закройщик" is not exactly a tailor but it's a related profession by the way.
1There's one more Russian word, кравчий "the head of the monarch's waiters, the servants at the monarch's dining table", probably a borrowing from the Polish krajczy with the same meaning, though. Still, the idea of cutting is present. Apr 22, 2020 at 14:57
@YellowSky yep, and if we want to go further, закрома, укромный, скромый are also related ) I might be wrong but as far as I remember Ukrainian "крок" is also related by the way.– shabunc ♦Apr 23, 2020 at 10:30
Ukrainian "крок" (а step) doesn't fit here, it's a cognate of "окорок" (ham, hind quarter) and "каракатица" (cuttlefish), all three from Proto-Slavic *korkъ (leg), cf. Bulgarian "крак" (leg). As for "закрома, укромный, скромный" I'm not sure, they have the root -кром- (also in "кромка") with the meaning "edge; to bite (as in "кромсать")". To bite and to cut have semantic affinity, but the sound is rather different from "kraj-/krav", as for me. Apr 23, 2020 at 12:57
@YellowSky oh, good to know about крок!– shabunc ♦Apr 23, 2020 at 12:58