1. Taru adjective, Adverb taking the 'to' particle

   vast (ocean, desert, etc.); boundless; extensive

   Usually written using kana alone

   その島の飛行場は、今では草がぼうぼうだ。

2. vague (e.g. memories); unclear; fuzzy; hazy

   Usually written using kana alone

3. rampant (weeds, etc.); running wild; overgrown

   Usually written using kana alone

4. unkempt (hair, beard, etc.); shaggy; scraggly

   Usually written using kana alone

Also written 茫茫【ぼうぼう】boubou