Moonbeam
Noun
げっこう
そのよるは、月光がとてもきれいでした。
The moonlight was very beautiful that night.
一りんの白い花に、月光がさえざえとふりそそいでいた。
The bright moonlight was beaming down onto a white flower.
月光に照らされた彼女は、とても美しかった。
She looked so beautiful in the moonlight.
The moon light (not sunlight!) can be bright sometimes. This is night when you're stumbling home from a nomikai after work. What is this light from the moon called? It's moon light. This word can also mean a moonbeam as well.
The reading is the on'yomi readings put together, though 月 is modified and shortened a bit. げつ goes to げっ. Make note of the different sized つ otherwise you'll be confused why you keep getting this one wrong over and over again!