From glosses on Herodotus 4.21, where he does indeed use the headword noun -- in the accusative case, as here -- in his survey of the territories beyond the river Tanais (web address 1).
The presence of "mixture" among the synonyms seems unwarranted.
The Ionic form is la/cis with a short alpha; the Attic is lh=cis (cf. lambda 465). The headword here with a circumflex accent confuses the two dialectal forms. This noun is related to the verb lagxa/nw.