The most common and most likely answer to this crossword clue is the 7 letter word NEUROMA
N
E
U
R
O
M
A
Buddy explains!
The straight part
We know that "tumour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tumour = neuroma.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 NEUROMA mean?
NEUROMA noun- A tumour composed of nerve cells.