The implied contrast in this sentence is not merely a matter of expecting one personality type and unexpectedly finding another.  Although that is certainly true, the boy’s mother is shocked at the character of the criminal activities.  In contrast with an innocent and upright childhood, these activities would not only be unexpected but also “nefarious,” meaning “wicked” or “criminal.”

The key to this sentence is to strike a balance between strict equivalence and opposition.   An equivalence would not provide the needed distinction, and there is nothing in the sentence to indicate a complete contrast.  The word “cognate” strikes just such a balance.  Although it usually describes words that are descended from the same linguistic roots, “cognate” can also mean “related” or “connected.” The word literally means “of the same birth” or “with+born.”  The “co[g]-” prefix means “with” (like “cohabitate” or “coordinate”).  The “-[g]nate-” portion is derived from Latin roots related to birth.  Similar English words are “nativity,” “natal,” and “nascent.”

Clearly, the sentence wishes to express the depth of Rembert’s voice, but this does not imply anything about its loudness.  Do not be fooled by the word “imposing.”  It is the depth that is compared to his imposing appearance.  The word “sonorous” implies depth and fullness to a voice, which well matches what is needed here. 

Although it is difficult to tell if the sentence is looking for a contrast to the word “discordant” or a synonym to it, it should be clear that none of the options can be a synonym in any strict sense.  The metaphor of being “discordant” implies that something “clashes” with the moralist’s experience.  Therefore, if it must be a contrast, the word “consonant” would work best, as it implies that something is “in agreement with” his experience.  Literally, to be consonant means to “sounds with” something else.  Two agreeing notes in a piece of music are considered to be “consonant.”  The usage here is metaphorical. 

Although it might seem that a rigid schedule is difficult, we cannot imply that directly. The word “regimented” best fits the needs of this sentence, meaning “strictly organized in a strict schedule.”  The word is related to a number of words for “ruling” such as “regal,” “regent,” and “regalia.”

There is nothing in this sentence to state that the king was arrogant in his demeanor even if he does distinguish himself from the general lot of people.  Although the necessary weaker sense might be expressed by “cultured,” the adjective “regal” likewise conveys the sense of “kingliness.”  The word is derived from the Latin word for king and is found in such English words as “regiment,” “regent,” and “interregnum.”

The contrast here is between “weak” and “strong” not “safe” and “dangerous.”  Therefore, the word “potent” is the best choice among our options.  “Potent” is related to a number of English words derived from the Latin for “to be able” as well as “power” such as “potency,” “possible,” “potential,” “omnipotent,” and “potentate.”

Although it might be tempting to choose one of the words related to old age, such as “senile” or “downtrodden,” it is necessary to pay heed to the key words “force and authority.”  While “defenseless” may seem to contrast this, it doesn’t match the sense as well as “impotent,” which directly signifies a lack of power.   It is derived from the “in-” prefix that means “not” (in this case) and “potent,” which means “having strength or power.”  The latter is derived from the Latin for “to be able” as well as other words meaning “power.”  Related English words are “potency,” “possible,” “potential,” “omnipotent,” and “potentate.”

Although William’s body is likely to be weak and fainting, all that we are told in the sentence is that he needs to be rehydrated (that is, replenished with regard to fluids, particularly water).  In such a case, it would be most appropriate to say that a person is “desiccated,” meaning that he or she is lacking fluid.  The word comes from the Latin root for “dry,” but it has few recognizable related words in English.  The word can also be used to indicate that one lacks passion or energy.

Although the professor’s words are likely endless and perhaps even academic or scholarly, the sentence wishes to indicate that they were a string of lifeless sources, strung together.  If something is (literally) dried out, it is said to be desiccated.  By extension, the term “desiccated” is applied to anything that lacks “sap” or vitality, even human words.