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tinder; touchwood; charcloth
「火口」 has other readings with different meanings.
ガスコンロの火口を掃除する必要がある。
I need to clean the gas stove burner.
この火口は火力が強くて料理がしやすい。
This burner has strong heat and is easy to cook with.
火口が詰まると火が均等につかなくなる。
If the burner is clogged, the fire won't ignite evenly.