Antonyms of adj undefendable

1 sense of undefendable

Sense 1
assailable, undefendable, undefended, open -- (not defended or capable of being defended; "an open city"; "open to attack")

INDIRECT (VIA vulnerable) -> invulnerable -- (immune to attack; impregnable; "gunners raked the beach from invulnerable positions on the cliffs")

Similarity of adj undefendable

1 sense of undefendable

Sense 1
assailable, undefendable, undefended, open -- (not defended or capable of being defended; "an open city"; "open to attack")
       => vulnerable (vs. invulnerable) -- (susceptible to attack; "a vulnerable bridge")