The most common and most likely answer to this crossword clue is the 5 letter word ILLER
I
L
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E
R
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The straight part
We know that "More sick" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case more sick = iller.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 ILLER mean?
ILLER adjective- Evil; wicked (of people).
- Morally reprehensible (of behaviour etc.); blameworthy.
- Indicative of unkind or malevolent intentions; harsh, cruel.
- Unpropitious, unkind, faulty, not up to reasonable standard.
- Unwell in terms of health or physical condition; sick.
- Having an urge to vomit.
- (hip-hop slang) Sublime, with the connotation of being so in a singularly creative way.
- Extremely bad (bad enough to make one ill). Generally used indirectly with to be.
- Unwise; not a good idea.