The most common and most likely answer to this crossword clue is the 5 letter word DROOL
I've seen this crossword clue in The Times
D
R
O
O
L
More clues leading to the result DROOL
- Master sent north to arrest old slaver
- Nothing left-leaning nobleman's penned is drivel
- Who perhaps can, on reflection, gloat?
- After reflection ruler imprisons old slaver
- Slaver keeping Australian native in confines of domicil
- Nobleman recalled hiding old slaver
- New or old slaver
- Slobber over visiting retired peer
- Peer retrospectively imprisons old slaver
- Slaver and doctor — gents that should be shown up
Buddy explains!

The straight part
We know that "gloat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gloat = drool.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 DROOL mean?
DROOL noun- Saliva trickling from the mouth.
- Stupid talk.
- To secrete saliva, especially in anticipation of food.
- To secrete any substance in a similar way.
- To react to something with uncontrollable desire.
- To talk nonsense; drivel.