井泉[seisen] (water) well
黄泉[kousen] underground spring
温泉[onsen] spa
九泉[kyuusen] hades
源泉[gensen] source

古泉学[kosengaku] numismatics
鉱泉[kousen] mineral spring
泉貨紙[senkashi] reclaimed paper
泉水[sensui] fountain

亜熱帯[anettai] subtropics
悪熱[onetsu] fever following a chill
稲熱[imochi] rice blight
稲熱病[imochibyou] rice blight
炎熱[ennetsu] sweltering heat

温熱[onnetsu] hot fever
温熱性[onnetsusei] thermal
下熱[genetsu] lowering fever
加熱[kanetsu] heating
火熱[kanetsu] heat (from a flame)