Compositional etymology, very interesting from the formal point of view. As a matter of fact, the second member is assumed to be an inflected form, namely, the dative plural of "all". Accordingly, the nominative δέπας is drawn from the dative δέπασι "given to all", and the inflected form is the starting point of the etymology (compare άρήν / ἀρά, βασιλεύς / πᾶς + λεύσσω, ἀγρός / ἀήρ, among others, and the alternative etymology for the same word δέπας / δύο + ὀπή). The first member is the root "to give", and it is not clear what form exactly is meant. The most likely hypothesis is that the starting point is the perfect δέδοται, where the initial δε- provides the initial syllable of δέπας. In that case, the first member of the compound would be identified with the reduplication. Alternatively, the starting point is either δι- of δίδωμι (still the reduplication) or δο- of δόσις, δοτός, which in modern terms is the root. In the latter case, the etymology requires a formal change of the vowel in order to provide the /e/ of δέπας. To my mind, the first hypothesis is more likely. At any rate, this etymology betrays a complete lack of morphological analysis by Greek authors save for Greek grammarians.