Completely
Entirely, Truly, Really, Wholly
adverb
This is the adverb version of the kanji all. So, it's like you add an 'ly' to it. But, that doesn't work too well (allly? c'mon). So, instead think of this word as completely, entirely or truly.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
The person who completely doesn't understand this vocab word is Matt (まった). Be sure to take note of the small っ, too.
全くできない
cannot do at all
全く分からない
to have no idea, to not understand at all
全く知らない
to not know at all
あなたと全く同じ考えです。
I have the exact same idea as you.
平日は全く休みが有りません。
There's no weekdays off at all.
全力でレバーを引いたが、水は全く出なかった。
I pulled the lever with all my strength, but there was no water coming out.