adjective · lacking in amount, quality, or required degree; a deficiency or state of being not enough

由于经费不足，那个项目被迫停止了。

verb, idiom · should not or is unable to (frequently used in formal constructions like "不足为 zú​yǐ​wéi...")

由于证据不全，他的证词不足为凭。

verb · not deserving of or meriting specific attention or action

这点小伤不足挂齿，你不必担心。