undefendable
1. [ adjective ] not defended or capable of being defended
Synonyms: open undefended assailable
Examples:

"an open city" "open to attack"

Related terms: vulnerable
Similar spelling:   undependable
  undefended
  undefinable
  undependably
  undeferential
  uneatable
  undefined
  undefiled
  undefeated
  undependability