The most common and most likely answer to this crossword clue is the 5 letter word DOBRO
D
O
B
R
O
More clues leading to the result DOBRO
Buddy explains!

The straight part
We know that "guitar" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case guitar = dobro.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 DOBRO mean?
DOBRO noun- An acoustic guitar with a metal resonator