From Wiktionary, the free dictionary
*갈- (*kal-, “to split?”) + -ᄋᆞ- (-o-, causative suffix). Compare 가리〮다〮 (kàlítá, “to get split”).
- (Morphophonemic) IPA(key): ⫽kàlʌ̀tá⫽
가ᄅᆞ다〮 (kàlòtá) (infinitive 갈아〮, sequential 가ᄅᆞ니〮)
- (transitive) to split
1481, 월인석보 (Worin Seokbo), volume 12, page 49a:갈아 두 乘이 ᄃᆞ외니 ᄒᆞᆫ 가지 아니오- kalG-a twu SUNG-i towoy-ni hon kaci ani-Gwo
- Since it became two by splitting it, it is not one.