a person of flighty and hasty character ...1563 obs.
from fling n. a spell of unrestrained indulgence of one's impulses + -brain
FIRST DOCUMENTED USE
1563 - see Example below
"...Remember what they haue bene which haue set forth
the same in this Realme: A sort of flyngbraynes and light heades,
which were neuer constant in any one thyng,
as it was to be seene in the turnyng of the Table"
From: Actes and Monuments of these Latter and Perillous Dayes
(The Book of Martyrs)
By: John Foxe, 1563
• A New English Dictionary on Historical Principles,
James Murray, 1887-1933