Able to be attacked or criticized; vulnerable to assault or challenge.
From assail (from Old French assaillir, from Latin ad- 'to' + salire 'to leap') + -able suffix. The word evolved to describe anything that can be attacked either physically or verbally.
Castle designers spent centuries trying to build walls that weren't assailable—but mathematically, any fortress with an entrance is technically vulnerable to attack, which is why medieval strategists focused on making assault so costly that attackers gave up.
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