Helmet – le casque
(Pronounced kask)
To remember that Helmet is pronounced kask (casque) in French, use the following mnemonic:
Her helmet looked like a whiskey cask (casque).

Casque is masculine, so it's le casque. Imagine the early learner using a helmet as a boat.

Examples of casque (helmet) in a sentence
Les motocyclistes doivent porter un casque pour leur sécurité.
(Motorcyclists must wear a helmet for their safety).
Elle portait un casque en fer comme précaution lors de la bataille.
(She wore an ironclad helmet as a precaution during the battle).
Les pompiers portent un casque spécial pour se protéger des débris.
(Firefighters wear a special helmet to protect themselves from debris).