LSJ
τά, (< τίθημι) foundations, lowest part, ὀφθαλμοῖο θ.
roots of the eye, Il. 14.493; στομάχοιο θ. 17.47; Ὠκεανοῖο θ. Hes. Th. 816; Ἄμμωνος θ.
the place where Ammon stands, i.e. his temple, Pi. P. 4.16; Παγγαίου θ.
the roots of Mt. Pangaeus, ib. 180; θ. δίκης Sol. 4.14; ἐκ θεμέθλων, Lat. funditus, Simm. 25.4; dub. in sg., Call. Dian. 248 (leg. θέμειλον).
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)