Emptiness or vanity — the opposite of substance and meaning. 'Empty hands' return from failed endeavors. The wicked are called req men — men of no substance, moral vacuity.
The emptiness theme runs from Genesis (the earth was 'formless and empty') to Ecclesiastes (all is vanity). Idols are riq — they promise fullness but deliver nothing (Isa 30:7).
Hebrew wisdom saw moral emptiness and ontological emptiness as connected. A life without God is literally riq — void, without weight. The NT's 'vain' translations echo this Hebrew foundation.