全く
まったく · mattaku · JLPT N3 · adverb
completely
全 = whole, complete; mattaku sounds like mat attack, a total takedown
The kanji 全 means whole or entire, as in 全部 (all of it). That is why 全く means completely. With a negative it means not at all, as in 全く分からない (I don't understand at all). On its own it can also mean really, or good grief.
全 — enter 入 on top + jade 玉
Originally written as 入 (enter) over 玉 (jade), depicting a complete, unflawed piece of jade kept in storage. From this image of a perfect jade came the meanings 'whole,' 'complete,' and 'entire.' The top component is sometimes written as 人.