熱 hot thing / fever

You don't want to get a fever form mosquito bites so put NETS around your bed at night.

They lit a fire all around the termite pie until it was a hot thing.

enthusiastic ★★☆☆☆
情 (emotion) + 熱 (hot thing / fever) = 情熱 (enthusiastic)

passionate! Although pretty far from how we'd use that word in english: the Japanese version means "dedicated , hardworking, diligent." 情熱な学生 (a passionate student) . . perhaps a better translation is simply 'enthusiastic.'

passionate ★☆☆☆☆
熱 (hot thing / fever) + 心 (heart) = 熱心 (passionate)

passion - usually used about sports or performances: They praised the actor's passionate performance. She's passionate about her hobby.

tropics ★☆☆☆☆
熱 (hot thing / fever) + 帯 (belt) = 熱帯 (tropics)

the tropics, tropical zone