From Proto-Indo-European *logʰos, from *legʰ- (whence also λέχομαι (lékhomai)). Cognates include Russian лог (log, “cleft, valley”), Polish odłóg, and Albanian lagje.
λέχος • (lékhos) (genitive λέχεος) n, third declension
- couch, bed
- marriage-bed: and generally, marriage
- a bird's nest
This inflection pattern originally had a sigma (i.e. *λέχεσος), which was dropped early on in the history of Ancient Greek.
The irregular accentuation of this paradigm is explained by the fact that it is the contracted version of the above paradigm.