完全【wánquán】

完全 goes before a verb or adjective and says there's no part left out. It fits verbs of knowing and agreeing, and adjectives like 一样, 正确 and 不同.

完全不 and 不完全

The place of 不 decides the meaning. 完全不 is "not at all"; 不完全 is "not entirely".

完全没 works the same way for something that didn't happen.

完全可以 says something is entirely possible or fine.

Not "all of it"

完全 describes a degree or state. For eating, finishing or using up everything, use 都 or a complement like 完.

• × 我完全吃了 → 我都吃了 / 我吃完了