Dictionary of Medieval Names
from European Sources

Helmdag m. Old High German, Old Saxon helm 'helmet' + Old Saxon, Old Dutch dag, Old High German tag 'day'.

Germany
Latin
822x875 Helmdag (nom) TradCorb §70
Cite as: S.L. Uckelman. "Helmdag". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2017, no. 1. http://dmnes.org/2017/1/name/Helmdag.