4 occurrences in 4 dictionaries

Reference: Helmet

Hastings

Morish

For the protection of the head, as worn by warriors. See ARMOUR. In the Christian's armour the helmet is 'salvation,' or 'the hope of salvation.' Eph 6:17; 1Th 5:8. It is those who know their salvation that can take part against the wicked spirits in the heavenlies. It is to be remarked that Jehovah (Christ) in a future day will Himself put on righteousness as a breastplate, and a helmet of salvation, to avenge His people by punishing their enemies. Isa 59:17.

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Smith

Helmet.

[ARMS]

See Arms, Armor