The most common and most likely answer to this crossword clue is the 12 letter word HINDQUARTERS
I've seen this crossword clue in The Times
H
I
N
D
Q
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A
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Buddy explains!

The straight part
We know that "Rear" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rear = hindquarters.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 HINDQUARTERS mean?
HINDQUARTERS noun- Either rear half of a side of beef, mutton, veal, lamb or by extension from another edible mammal.
- (in the plural) The hind biped (leg) of a quadruped, or all body parts situated behind the hind legs' trunk-attachment.
- (metonymy, usually plural) Human behind, butt.