大毘盧遮那成佛經疏 1.4

1.4

「成佛」者，具足梵音應云成三菩提，是正覺正知義。謂以如實智，知過去未來現在、眾生數非眾生數、有常無常等一切諸法皆了了覺知，故名為覺。而佛即是覺者，故就省文但云成佛也。

As for "abhisaṃbodhi" (becoming a Buddha): fully expressed in Sanskrit, it should be attaining saṃbodhi, which means correct awakening and correct knowledge. That is to say, by means of knowledge of reality, knowing past, future, and present, whether included among sentient beings or not included among sentient beings, permanent or impermanent—all such dharmas are clearly and completely awakened to and known; hence it is called awakening. And since the Buddha is precisely the awakened one, for the sake of brevity the text merely says "becoming a Buddha".