From a (as a negative particle) and dunatos; unable, i.e. Weak (literally or figuratively); passively, impossible -- could not do, impossible, impotent, not possible, weak.
see GREEK a
see GREEK dunatos
1. without strength, impotent: τοῖς ποσί, Acts 14:8; figuratively, of Christians whose faith is not yet quite firm, Romans 15:1 (opposed to δυνατός).
2. impossible (in contrast with δυνατόν): παρά τίνι, for (with) anyone, Matthew 19:26; Mark 10:27; Luke 18:27; τό ἀδύνατος τοῦ νόμου 'what the law could not do' (this God effected by, etc.; (others take τό ἀδύνατος here as nominative absolutely, cf. Buttmann, 381 (326); Winer's Grammar, 574 (534); Meyer or Gifford at the passage)), Romans 8:3; followed by the accusative with an infinitive, Hebrews 6:4, 18; Hebrews 10:4; by an infinitive, Hebrews 11:6.