Vain, Groundless, Futile
noun, な adjective
The sky has an air of neglect about it and makes it seems like everything you're doing is in vain. Why even bother? The sky doesn't even believe in you.
くうそ
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
こんな空疎な論争を続けるのは時間の無駄だ。
Continuing such a futile dispute is a waste of time.