The most common and most likely answer to this crossword clue is the 8 letter word SQUATTER
I've seen this crossword clue in The Guardian
S
Q
U
A
T
T
E
R
More clues leading to the result SQUATTER
- Illegal occupier of property is more stocky
- Illegal resident is comparatively thick
- . Relatively short and thick uninvited guest
- Dumpier person in illicit occupation
- He settles without recourse to law
- Unlawful occupant, stockier
- Quartets playing for uninvited resident
- Illegal occupant, short and stocky, they’re regularly chasing
- One who can’t stand being in another’s house?
- More stout, in a smaller package, needed for unwanted guest
Buddy explains!

The straight part
We know that "Dumpier/person in illicit occupation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dumpier/person in illicit occupation = squatter.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 SQUATTER mean?
SQUATTER noun- One who squats, sits down idly.
- One who occupies a building or land without title or permission.
- A large-scale grazier and landowner.
- A squat toilet.