Compositional etymology, semantically fantastic. In the commented line, λιαρός is used as epithet of ὕπνος "sleep", which cannot be "tightly adapted". Therefore this etymology was designed for a different context, presumably one where the adjective applied to a garment. A plausible hypothesis is that we are dealing with a transfer of the etymology of χλιαρός to λιαρός, since the latter was often derived from the former (see λιαρός / χλιαρός). Χλιαρός is itself related to (and derived from) χλιαίνω "to warm", which is assumed to be the etymon of χλαῖνα "coat", an old etymology going back to the first c. AD at least (see χλαῖνα / χλιαίνω). The coat is a garment, and, tightly adapted (λίαν ἀρηρότα), it keeps the body warm (θερμαίνει τὸ σῶμα)