Bailly
ὑπό·γειος, ος, ον, c. ὑπόγαιος, PLAT. Ax. 371 a ; TH. (ATH. 61 e) ; POL. 34, 10, 4 ; PLUT. M. 779 f ; LUC. Philops. 34, etc. ; τὸ ὑπ. PLUT. M. 770 e, etc. chambre souterraine.
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LSJ
also ὑπόγαιος, ον, (< γῆ) underground, subterraneous, οἴκημα ὑπόγαιον Hdt. 2.100, 148 (vv. ll. -γεον, γεα) ὀρύγματα ὑπόγαια mines, Id. 4.200 (v.l. -γεα)· ὑπογαίου (v.l. -γείου) βροντῆς A. Fr. 57.10 (anap.); ὑπόγειον ὕδωρ Gp. 2.6.33; ὑ. οἶνος stored in a cellar, Gal. 19.95. ὑπόγειον or -γαιον, τό, an underground chamber, Plu. 2.770e, Hdn. 1.15.6. Astron., under the earth, Man. 3.27, Gp. 1.7.1; [ἄστρα] τὴν ὑ. φορὰν ἐνεχθέντα Placit. 1.6.8; τὸ ὑ.
the nadir, Vett.Val. 75.24. — The form ὑπόγεως, ων, cited in Hdn. Epim. 208 and Suid., occurs in codd. of Paus. 2.2.1, 2.36.7; cf. ὑπογάιδιον.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
Pape
unter der Erde, unterirdisch ; Aesch. frg. 51, wie Strab. 10.3.16, wo Cramer ὑπογαίου schreibt ; Plat. Ax. 371a ; Luc. u. a.Sp. S. ὑπόγαιος und ὑπόγεως.
Pape, Griechisch-deutsches Handwörterbuch (3. Aufl., 1914)