ἀμφίκοιλος
From LSJ
Ὁ μὲν βίος βραχύς, ἡ δὲ τέχνη μακρή, ὁ δὲ καιρὸς ὀξύς, ἡ δὲ πεῖρα σφαλερή, ἡ δὲ κρίσις χαλεπή → Life is short, art long, opportunity fleeting, experience misleading and judgment difficult
English (LSJ)
ον,
A hollowed on both sides, Suid. II doubly concave, of a curvilinear angle, Procl.in Euc.Def.8p.127F., al.