Precious
Valuable
noun, な adjective
Something that's valuable and heavy is extremely precious and probably even more valuable than your less heavy things.
This is a jukugo word that uses the on'yomi readings of the kanji. You didn't learn this reading for 重 though, so here's a mnemonic to help you:
Keep things precious to you very close, because the evil Mrs. Chou (ちょう) will come and steal it away if you don't. She'll take every valuable you have and destroy them.
貴重なご意見を有難うございます。
Thank you for your valuable opinions.