Probably
Perhaps, Likely, I Dare Say, Maybe, As Likely As Not
adverb
A fear rock (らく) will probably come straight at your face. It's pretty likely.
おそらく
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!
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.