The most common and most likely answer to this crossword clue is the 1 plus 2 plus 1 letter word A TO Z
A
T
O
Z
More clues leading to the result A TO Z
Buddy explains!
The straight part
We know that "a guide" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a guide = a to z.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.