The most common and most likely answer to this crossword clue is the 3 plus 4 letter word LES PAUL
I've seen this crossword clue in The Daily Telegraph
L
E
S
P
A
U
L
More clues leading to the result LES PAUL
Buddy explains!

The straight part
We know that "Famous guitarist" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case famous guitarist = les paul.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.