Perhaps, Likely, I Dare Say, Maybe, As Likely As Not
Adverb
おそらく
犯人は恐らくこの辺りに潜んでいるのでしょう。
The criminal is probably lurking in this area.
A fear rock (らく) will probably come straight at your face. It's pretty likely.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You learned this reading already so you should be able to read it!