The most common and most likely answer to this crossword clue is the 8 letter word RED-CARD
I've seen this crossword clue in The Times
R
E
D
-
C
A
R
D
Buddy explains!
The straight part
We know that "Dismiss" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dismiss = red-card.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 RED-CARD mean?
RED-CARD verb- To show (a player) a red card, and dismiss them from the playing area; to send off.