This form of the headword, the nominative singular masculine/feminine, is unattested outside lexicography; however, plural forms occur frequently in hexameter poetry, in the formula xei=res a)/aptoi or xei=ras a)a/ptous (usually interpreted as 'irresistable hands'); e.g. Homer, Iliad 8.450 (web address 1).
[1] The etymological comments that follow occur only in mss G (= Parisinus 2623) and T (= Vaticanus 881); cf. Herodianus 3.2.30.
[2] This etymology, alpha-privative + a(/ptomai ('touch'), is the one most commonly accepted nowadays. See LSJ s.v. (web address 2) and Schwyzer, DGE. Yet there is reason for doubt, and the correct Homeric form (attested already by Aristophanes of Byzantium) may actually be a)ept-. See Chantraine s.v. a)/aptos.

A word from epic poetry, e.g. Homer, Iliad 5.892 (web address 1), with metrical reduplication of the initial alpha (cf. LSJ s.v. a)/sxetos at web address 2). The headword and the gloss are both masculine/feminine nominative singular.
[1] A related but not identical word (a)katakra/thton) is used to gloss the neuter form of the headword at Etymologicum Magnum 1.32.

The headword is the third person plural, aorist indicative active, of a)bake/w. This form is found only in Homer, Odyssey 4.249 (web address 1), and the many lexicographical notices generated by it. Of those the most similar to this entry are Photius, Lexicon alpha22 Theodoridis, and Etymologicum Magnum 2.30-31. Compare also Apollonius Sophistes, Homeric Lexicon 2.16; Hesychius alpha54. The glosses offered here and elsewhere probably represent semantic extrapolation from the Homeric context: When Odysseus comes in disguise to Troy, Helen knows who he is but the rest of the people in Troy a)ba/khsan. The translation of the headword, on the other hand, reflects the verb's probable etymological connection with the verb ba/zw 'speak', and the adjective a)bakh/s ('speechless', 'tranquil'). Cf. Chantraine s.v. a)bakh/s, a connection that is sometimes mentioned as a possibility in the ancient scholarship.