1. Lacking seriousness; given to frivolity
   - airheaded, dizzy, featherbrained, giddy, light-headed, lightheaded, silly

See also: frivolous

• unaffordable
• unaffordablity
• unafraid
• unaged
• unageing
• unaggressive
• unaging
• unagitated
• unai
• unaided
• unaired
• unairworthy
• unalarming
• unalert
• unalienable
• unaligned
• unalike
• unalloyed
• unalterability
• unalterable
• unalterably
• unaltered
• unambiguity
• unambiguous
• unambiguously