The most common and most likely answer to this crossword clue is the 6 letter word FUNGUS
I've seen this crossword clue in The Daily Telegraph
F
U
N
G
U
S
Buddy explains!
The straight part
We know that "Growth" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case growth = fungus.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 FUNGUS mean?
FUNGUS noun- Any member of the kingdom Fungi; a eukaryotic organism typically having chitin cell walls but no chlorophyll or plastids. Fungi may be unicellular or multicellular.
- A spongy, abnormal excrescence, such as excessive granulation tissue formed in a wound.