The most common and most likely answer to this crossword clue is the 5 letter word FAMED
F
A
M
E
D
Buddy explains!
The straight part
We know that "Well-known" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case well-known = famed.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FAMED mean?
FAMED adjective- Having fame; famous or noted.