Compositional etymology relying on the meaning of the middle ἅπτομαι "to touch". The initial [l] is parsed as the intensive prefix λα-. Therefore "to lap", "to drink eagerly" would be a specialization of "to touch impetuously (water)". The etymology remains anonymous in Orion and is not listed in Thodoridis' edition of Philoxenus. However, the use of λάπτω as etymon of λαίλαψ and λάβρος in Philoxenus implies that this was his analysis of λάπτω (see λάβρος / λα- + ἅπτω), therefore the etymology goes back at least to him, although it may be older.