really

1 ENTRIES FOUND:
really /ˈriːjəli/ adverb
really
/ˈriːjəli/
adverb
Britannica Dictionary definition of REALLY
1 
— used to refer to what is true or real
2 
: without question or doubt — used to make a statement more definite or forceful
3 
: to a great degree : very
4 
— used to reduce the force of a negative statement
5 
— used in speech to show surprise, doubt, or interest
6 
US — used in speech to express agreement with what someone has just said
7 
— used in speech to show that you are annoyed

not really

— used to say “no” in a way that is not very forceful or definite