The headword is the aorist subjunctive active, third person dual, of the verb mata/w, I hesitate, dally, am idle; see LSJ s.v. It may also mean I do nothing, act in vain in this context (Kirk, p. 84). The headword occurs at, and is taken to be quoted here from, Homer, Iliad 5.233 (web address 1): Pandarus (OCD(4) s.v.) advises Aeneas (OCD(4) s.v. and alphaiota 214) to drive his own chariot into battle, lest the two horses take fright at some critical moment, and thus, without their master's presence, would hesitate to carry the men out of the battle. The verb mata/w is used of horses that, having grown restive, shirk their work (Cunliffe, p. 256).
[1] The gloss is the aorist subjunctive active, third person plural, of the verb a)mele/w, which as an absolute means I am careless, negligent; see LSJ s.v. and cf. Hesychius s.v. ma/thsen (he/she/it hesitated; aorist indicative active, third person singular, of mata/w; instanced at Homer, Iliad 23.510 (web address 2)). Adler also cites the Ambrosian Lexicon (245).