Derivational etymology. It is semantically straightforward since, indeed, λακτίζω is the denominative of λάξ, as was correctly acknowledged by some authors (see λακτίζω / λάξ). The problem is that it was thought to be formally difficult because of the syncope it implies: from λακτίζω one derives an adverb *λάκτιξ (a ghost form invented as an intermediate step for the sake of the etymology), and then by syncope the attested л;ай: This is why this etymology is discarded in favor of an alternative one, going back to Philoxenus, and mentioned in the second part.