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.
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!
それは恐らく本当のことだと思います。
I think that's probably true.
彼は恐らくそのニュースを知っているはずです。
He probably knows about the news.
恐らくこれが最後のチャンスでしょう。
This is probably the last chance.
犯人は恐らくこの辺りにひそんでいるのでしょう。
The criminal is probably lurking in this area.