sicker
For the word "sick, the comparative is "sicker" and the superlative is "sickest."
"Litter" is a noun and a verb and, as such, does not have a comparative degree.
more out
more out
better for its comparative and best for its superlative
The comparative degree is 'more magnificent' and the superlative degree is 'most magnificent'.
abler
nicer
finer, finest
greedier, greediest
More is comparative. The progression is many, more, most
The comparative degree of the word greedy is greedier (reference: wordweb dictionary).