• gasmask,
• gazmask,
• gassmask,
• gasmark,
• fas mask,
• vas mask,
• has mask,
• yas mask,
• tas mask,
• gzs mask,
• gss mask,
• gws mask,
• gqs mask,
• gaa mask,
• gaz mask,
• gax mask,
• gad mask,
• gae mask,
• gaw mask,
• gas nask

The adjective form of "gas mask" is "gasmasked".

The plural form of "gas mask" is "gas masks".

The singular form of the word "Gas Mask" is "Gas Mask". The word does not change when referring to a single item.