N3
なかなか~ない
Not easily, Just won't, Takes a long time to
仕事が忙しくてなかなか休みが取れないんだよね。
Work is so busy that I just can't take time off.
Explanation
「なかなか~ない」 means 'just won't, not easily'. You want something to happen or get done, but something gets in the way and it keeps not happening: 「風邪がなかなか治らない」 (My cold just won't go away), 「バスがなかなか来ない」 (The bus is taking forever to come). It carries impatience or frustration.
Mixed up with
「なかなか~ない」 is 'wanted, but it doesn't work out'. 「全然~ない」 is 'not at all': 「全然勉強しない」 (never studies). 「あまり~ない」 is 'not very'.
It can't be used for things that were never going to happen. Don't say 「×冬にはなかなか桜が咲かない」.