SCATTERBRAINED
flighty, flyaway, head-in-the-clouds, scatterbrained
(adjective) guided by whim and fancy; “flighty young girls”
rattlebrained, rattlepated, scatterbrained, scatty
(adjective) lacking sense or discretion; “his rattlebrained crackpot ideas”; “how rattlepated I am! I’ve forgotten what I came for”- Glenway Westcott
Source: WordNet® 3.1
Etymology
Adjective
scatterbrained (comparative more scatterbrained, superlative most scatterbrained)
Having the qualities of a scatterbrain: absent-minded, forgetful, easily distracted.
Source: Wiktionary
Scat"ter-brained`, a.
Definition: Giddy; thoughtless.
Source: Webster’s Unabridged Dictionary 1913 Edition