窃 is a bound morpheme (b.f.) that cannot stand alone as a word; it appears in compound words. Its core meanings are 'to steal' (盗窃, 窃取) and 'secretly, stealthily' (窃听, 窃笑). It also functions as a humble prefix in formal writing, equivalent to 'I' in self-deprecating expressions, most commonly in 窃以为 ('in my humble opinion').