STEP Greek Lexicon: ὑποζύγιον

ὑπο-ζύγιος, -α, -ον

[in LXX for חֲמוֹר ;]

under the yoke; as subst., τ . (Hdt., al.), a beast of burden; colloq., an ass (see Deiss., BS, 160 f.), and so always in LXX and NT: Mat.21:5 (LXX), 2Pe.2:16.†

(AS)