The Ugaritic word is best attested in the reduplicated combination dr dr ‘eternity’ in KTU 1.2 IV 10 and KTU 1.19 III 48.
The – apparently iconic (descriptive) – reduplication *dār- dār- (or *dār- dawr-), attested in both Akkadian and early NWS (Ugaritic, Hebrew, Aramaic), may go back to PS.