To Be Luxuriant, To Grow Thickly
intransitive verb, godan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means luxuriant and the verb vocab version is to be luxuriant or to grow thickly.
しげる
She gave (しげ) me a razor because my beard was starting to grow thickly... too thickly. But, I won't shave my awesome beard no matter what she gave me.
妖婆の庭には雑草が生い茂っていた。
The hag’s garden had grown thick with weeds.