unhelmetv.
Etymology: un- prefix2 1b.Previous versions of the OED give the stress as: unˈhelmet.
society > armed hostility > military equipment > armour > helmet > wear helmet [verb (reflexive)] > take off helmet
1823 W. Scott II. v. 113 He was compelled to dismount..and unhelmet himself.
This entry has not yet been fully updated (first published 1924; most recently modified version published online June 2019).