12th cent. Old Spanish lexar 'id.' Roberts (2014) argues that dejar replaced l- with d- under influence from dar, but this does not explain why d-initial cognates abound in Romance. Far more evincing from Penny (2002) is that lexar represents a learned form from Latin laxare, wheras dejar comes from Vulgar Latin *daxare 'id.' From Latin laxare "to relax" with the l- replaced with d- under influence from Oscan. From the noun laxus (see laja).
Romance: Western Vulgar Latin: Asturian dexar, Portuguese deixar, Galician deixar, Catalan deixar, French laisser, Italian lasciare; Eastern Vulgar Latin: Aromanian lãsari, Romanian lăsare; Sardinian lassare