The most common and most likely answer to this crossword clue is the 10 letter word POOH-POOHS
I've seen this crossword clue in The Guardian
P
O
O
H
-
P
O
O
H
S
Buddy explains!
The straight part
We know that "Dismisses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dismisses = pooh-poohs.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 POOH-POOHS mean?
POOH-POOHS verb- To dismiss idly with contempt or derision.