The superlative of slim is slimmest.
skinnier, skinniest
Thinnest
thinner, thinnest
thinner, thinnest
thinner, thinnest
Thinnest is the superlative degree of thin.
thinnest
thinner
thinner, thinnest
thinner, thinnest
Superlative to "More" is the word, "Most".
There is no procedure (except maybe looking it up in the dictionary, if you don't know on your own). The comparative of thin is thinner; the superlative is thinnest.
what is the superlative word for blue