谚 (yàn) is a bound morpheme (b.f.) that does not stand alone; you always find it as part of the compound 谚语 (yànyǔ, 'proverb, aphorism'), which refers to a traditional, widely circulated saying that conveys folk wisdom. Note that 谚 itself does not mean 'metaphor' — that concept is expressed by 比喻 (bǐyù). In writing, 谚 appears only inside longer expressions like 农谚 (nóngyàn, 'farming proverb') or 古谚 (gǔyàn, 'ancient saying').