Frequency: The word is one of the 700 most common words in English.
1.
If you say that something is probably the case, you think that it is likely to be the case, although you are not sure.
The White House probably won't make this plan public until July...
Van Gogh is probably the best-known painter in the world.
ADV: ADV with cl/group [vagueness]
2.
You can use probably when you want to make your opinion sound less forceful or definite, so that you do not offend people.
He probably thinks you're both crazy!
ADV: ADV with cl/group [vagueness]