While searching on google, I`ve found out that only is a focusing adverb.
These are used to allow the speaker to focus on a particular element in a clause: even, only, just, especially, particularly, etc.
The focusing adverb is typically placed immediately before the focused element: Only John tasted the soup. However, depending on the placement of sentence stress, only can focus on either tasted or the soup in John only tasted the soup.
source:HF ENG 111 Grammar: Lecture 13