thinnest
Thinnest is the superlative degree of thin.
thinner
Thinnest
thinner, thinnest
thinner, thinnest
Thinnest is the superlative degree of thin.
Comparative: thinner Superlative: thinnest
The superlative of slim is slimmest.
thinner
Thinnest
thinner, thinnest
thinner, thinnest
thinner, thinnest
thinner, thinnest
thinner, thinnest
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.
The superlative form of "thin" is "thinnest." It is used to describe something that has the least thickness or is the slimmest among a group. For example, you might say, "She is the thinnest person in the class."