The most common and most likely answer to this crossword clue is the 10 letter word BELLY-FLOP
I've seen this crossword clue in The Guardian
B
E
L
L
Y
-
F
L
O
P
Buddy explains!
The straight part
We know that "terrible dive" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case terrible dive = belly-flop.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 BELLY-FLOP mean?
BELLY-FLOP noun- A style of diving into a body of water in which the surface impact is made mostly by one's abdomen.