question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

furnace, kiln

key (tool for opening or locking something) / key; clue (important fact for solving something) / lock

(computing) key / (music) key

furnace, kiln, reactor

key

nuclear / atomic / nuclear power / core / kernel

energy conservation; energy saving

alternative energy, substitute energy

Synonym of 位置エネルギー (ichi enerugī, “potential energy”)