Although the word “hearty” is somewhat like “hardy,” meaning “robust or strong,” it is most often used to indicate “healthy or lively” in a more metaphorical sense, as when we say, “A hearty smile.” Such a smile is cheerful and strong. In opposition to such vigorous and lively smiling, we can consider the “restrained” person, that is, one who is moderate and understated.

A cantankerous person has an ill temper and often argues. We often think of “cantankerous old men,” though there are indeed cantankerous young people as well. In contrast with such an argumentative personality, the word “affable” is an excellent antonym. Someone who is affable is good-tempered, friendly, and agreeable.

In its most general (and literal) sense, “infidel” means “someone who is unfaithful,” generally implying that this lack of faithfulness pertains to religious matters. The “-fidel” portion of the word comes from the Latin for “faith” or “faithful,” as found in the English “fidelity” and the Marines’ motto “semper fidelis”—always faithful. Among the options provided, only “believer” adequately expresses an antonym to infidel. 

When two things are identical, they are exactly the same in some respect. It comes from the Latin for “the same.” To “identify” something is to say that the thing is the same as your description. The best antonym for “identical” found among the options provided is “dissimilar,” meaning “not alike.”

Although “lust” means “an extreme (often immoral) desire,” the word “lusty” is derived from an earlier sense of “lust” as “strength or vigor.” (You can see this even in the fact that “lust” is used to describe a strong desire or attraction). The word “lusty” thus means something like “strong, vigorous, or healthy.”  In contrast to such lustiness, “sickly” is by far the best antonym among the options provided.

Do not be tricked by the many synonyms found among the answers—nasty, unkind, signify, and moderate. The word “mean” has a number of meanings, from “to signify” to “nasty” to “average” (as in an arithmetical mean). The word can also mean “not giving or generous.” Thus, the best antonym is “generous.” All of the others are good synonyms for various senses of the word.  However, that does little good when you are looking for an antonym.

The word meager is derived from root words meaning “thin” in the sense of not being physically fat. When supplies, food, or other things are described as being “meager,” they are lacking in quantity. Among the options provided, the only antonym to such lack is “plentiful.”

When something is nefarious, it is gravely wicked or criminal. Generally, the word is used to describe some action. For instance, one could say, “The group of young mobsters committed a number of nefarious murders that were reported throughout the nation due to the cruel manner by which they killed their victims.” In contrast to such wicked actions, “righteous” actions are “right” in the strong, moral sense.

When someone “registers an objection,” that person expresses opposition to some point of view, fact, etc. To say, “I object . . .” is akin to saying, “I disagree . . .” In contrast to objection, “concurrence” is the state of being in agreement. It literally means “to run with,” as though to say, “to be going in the same direction.” The current of a stream is the “running” of the water in the stream. To say, “I concur,” is basically the same as saying, “I agree with you.”  “Concurrence” is thus an excellent antonym for “objection.”

"Recent," "renege," and "forswear" are synomyms of abjure. "Abjure" means to renounce or give up under oath. "Emphasize" means to lay stress upon something.