noun, noun which may take the genitive case particle 'no'
absentmindedness; dreaminess; carelessness
Dated term for a state of being spaced out, dreamy, or not paying attention. Often used in historical or literary contexts.
hollowness; emptiness
Rare, dated sense referring to literal or figurative emptiness. Mostly found in older texts.
He was staring out the window with an absentminded look.
That man is a fool.
The jar made a hollow sound.
Usually written in kana.
Kanji spelling using 虚 (void, hollow); rare and literary.
Kanji spelling using 空 (empty); rare and literary.
The exact derivation is uncertain. It may be related to 空 (うつ, 'hollow') or 虚 (うつ, 'void'), with the suffix け indicating a state or quality. The word is now dated.