Antonym of "superlative"

I would think that the word superlative would not have an antonym. Rather, the opposite of a superlative for a given adjective would be to use the antonym of that adjective in its corresponding superlative form. For example, the word thick has as its superlative the word thickest. There is no word lesser than the word thick: the adjective is already in its most minimal state. To express the opposite of thickness, one would use the term thin, and its superlative form thinnest. One could say less thick and least thick, but that would be grammatically awkward.

The superlatives used by hack movie reviewers may be thought of as a form of hyperbole. The opposite of that would be something like understatement:

understatement |ˈəndərˌstātmənt|
noun the presentation of something as being smaller, worse, or less important than it actually is
[NOAD]

A pejorative (also called a derogatory term, a term of abuse, or a term of disparagement) is a word or grammatical form expressing a negative connotation, a low opinion of someone or something, or showing a lack of respect for someone or something. It is also used as criticism, hostility, disregard and/or disrespect.
—“Pejorative”, Wikipedia, the free encyclopedia

Consider the following statement.

One of the presidential candidates in the 2016 campaign consistently resorts to the use of alternating superlative and pejorative statements.

The dictionary definition of the noun 'superlative', in the context in which you're using it, is "the superlative form of an adjective". The superlative form of an adjective is basically the 'most positive' form. Based on that definition, the best antonym that can be used as a noun I can think of is negative, or perhaps insult.

Sublative also seems like a good candidate and is a literal antonym of superlative, but it seems to be quite rare and so people might not understand the word's meaning.