unflutterableadj.
Etymology: Previous versions of the OED give the stress as: unˈflutterable.
the world > movement > progressive motion > moving with current of air or water > motion in the air > [adjective] > fluttering > that cannot be fluttered
1871 A. D. Whitney viii The quiet, unflutterable gray bonnet calmly horizontal.
This entry has not yet been fully updated (first published 1921; most recently modified version published online June 2019).