The most common and most likely answer to this crossword clue is the 12 letter word BRONTOSAURUS
B
R
O
N
T
O
S
A
U
R
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S
Buddy explains!
The straight part
We know that "Vegetarian" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vegetarian = brontosaurus.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 BRONTOSAURUS mean?
BRONTOSAURUS noun- One of the largest land animals to ever walk the earth; a Brontosaurus.