Capable of being frustrated or thwarted; able to be prevented or foiled.
Formed from 'frustrate' plus the suffix -able (capable of being). This is a logical construction following standard English word-formation patterns, though it's rarely used.
English lets us add -able to almost any verb, but just because we *can* create a word doesn't mean people will use it—'frustrable' exists grammatically but almost never appears in real writing!
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