To Conceal, To Keep Secret
transitive verb, ichidan verb
If you secret something, you are trying to keep secret something. That, or you're trying to conceal it.
ひめる
The reading is the same as the one you learned with the kanji, strangely enough. Nothing to conceal about this reading, you gots it.
彼は内に秘めるタイプなので、心配しています。
I’m worried about him because he tends to hide his feelings.