吐字 is a separable verb (离合词) that means 'to enunciate' or 'to articulate words clearly', especially in speech, acting, or singing. The verb 吐 and the noun 字 can be separated by measure words or complements: you say 吐字清楚 (enunciates clearly) when combined, but can insert elements like 吐一个字 ('pronounce one word') or 吐得清楚 ('enunciate clearly' with a potential complement). The object of enunciation is built into the compound—you don't add a separate object after 吐字.