The most common and most likely answer to this crossword clue is the 5 letter word POOCH
P
O
O
C
H
More clues leading to the result POOCH
Buddy explains!

The straight part
We know that "Dog" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dog = pooch.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 POOCH mean?
POOCH noun- A dog.
- A dog of mixed breed; a mongrel.
- A bulge, an enlarged part
- A distended or swelled condition.
- To distend, to swell or extend beyond normal limits; usually used with out.