Henry George Liddell, Robert Scott, A Greek-English Lexicon

A.diametrical: Astrol., diametrically opposed, Ptol.Tetr.115, Man.1.89.

II. Subst. δ. (sc. γραμμή), ἡ, diagonal of a parallelogram, Pl.Men.85b,al.; κατὰ δ. συντίθεσθαι, of triangles, by the hypotenuses, Id.Ti.54d; diameter of a circle, Arist.Cael.271a12, etc.; axis of a sphere, Id.MA699a29; diameter of other curves, Apollon.Perg.Con.1Def.1; axis of a conic, Archim.Aequil.2.10; ἡ κατὰ διάμετρον σύζευξις, of circles, Arist.EN1133a6; “τὰ κατὰ δ.” Id.Cael.277a24; “κεῖσθαι κατὰ δ.” Id.Mete.363a34, al.; κατὰ δ. κινεῖσθαι, of quadrupeds, which move the legs cross-corner-wise, as horses when trotting (opp. κατὰ πλευρὰν κινεῖσθαι ambling, in which the legs on either side move together), Id.HA490b4, IA712a25, cf. Plu. 2.43a; ἐκ διαμέτρου ἀντικείμενος, of planets, in opposition, PMag. Par.1.2221; “ἐκ διαμέτρου ἡμῖν οἱ βίοι” Luc.Cat.14.

2. prob. mitre-square, Ar.Ra.801.