All of these options are in some way related to the provision of light for some area or surface. To “illuminate” something is to shine a light upon it. It literally means “to place light onto.” Light bulbs are rated as having a certain number of “lumens.” Lumens are units of light production—as opposed to mere power consumption as expressed by “watts.” The one word that is different among those provided is “effulgent,” which means “brightly shining.”  Even “brightened” might only mean that something has been relatively brightened—e.g. from dark grey to light grey; however, “effulgent” always indicates the state of strong or extreme brightness. Thus, the word differs from the others.

All of the related words in this group describe easiness of some sort.  Likely you have no problem seeing that in “easy,” “undemanding,” and effortless. The word “facile” means “easily accomplished.” A “facile undertaking” is one that is very easy (and likely not very impressive either). Often, the word carries an implication like, “It was very easy—an hence not worth praise.” Something is “onerous” when it is very difficult.  It comes from the Latin “onus” meaning “burden or load.” When someone is “exonerated,” he or she is declared innocent in a court hearing. That person can be said to have had the “burden of guilt” lifted from him or her.

All of the related words describe some relationship between lines. Two parallel lines are ones that have the same slope and hence never meet. Skew lines are ones that never meet at all—but in three-dimensional space. Perpendicular lines are those that meet at 90-degree angle. Of course, “intersecting” pertains to lines!  “Elliptical,” while geometrical, does not necessarily pertain to linear matters.

All of the related words describe types of trees. This is blatantly obvious in the case of “pine” and “oak.” A coniferous tree is a tree that has needles and cones. Literally, the word means “cone bearing” or “cone carrying.” The “-fer” portion can be found in words like “transfer,” meaning “to carry across,” and the name “Lucifer” of Judeo-Christian mythology, meaning “the light-bearer.” Deciduous trees are those that have leaves that fall every autumn. In contrast, “perennial” means either “lasting forever.” It can be applied to plants to mean those plants that you do not have to replant each year; however, in neither of these cases does the word strictly apply to trees as do the others.

The set of related words all have to do with some level of interiority or privacy. The word “mental” can be included here because it indicates things that are kept “in the mind” in contrast to things that have been expressed. Likewise, something “personal” can be contrasted to something “public,” as when we say, “That is a personal matter and not appropriate for public discussion.” The word “communicated” expresses some degree of being “external” that is different from all of these other words.

Note that all of the related words pertain to something being insignificant. When something is “inconsequential,” it is of little meaning—as though it were “of little consequence.” While “immaterial” could mean “spiritual” (like ghostly “immaterial substances”), it likewise can merely indicate that something is unimportant in a given set of circumstances. (It just doesn’t matter!). A “trifle” is a small thing, so a trifling matter is an unimportant one. Something that is negligible is so important that it is “neglect-able.” “Significant” stands in opposition to all of these options.

All of the incorrect answers are somehow related to the word “implicit,” which means “not expressed openly or fully.” While something “explicit” is “spelled out” completely, “implicit” (or “implied”) matters are hidden and “unspoken.” Sometimes what we say can have implied meanings that are not directly stated—often leading to misunderstandings and disagreements when people misunderstand the implied remarks. Things “latent” are hidden and undeveloped—a notion at least similar to being implicit. “Indirect” is related to the sense of implying discussed above—indirectly communicating something in addition to the explicit meaning. Something “unstated” may still be implied even though it is not explicitly stated.

All of the related words pertain in some manner to the notion of being important. Something that is “consequential” can be thought of has “having consequences” (hence, being important). A “weighty” matter is not necessarily one that is physically heavy. The word is often used to describe something that is important—it has great weight metaphorically. A momentous occasion is one that is of great importance, often implying that its importance will influence the future in some way. Something “trite” is overused and thus ignored and generally unimportant. A trite expression of comfort is one that is so used that it really has no meaning and hence provides little or no comfort.

Perhaps the easiest way to see this answer is to realize first that “abstract” means “pertaining to an idea but removed from actual reality.” It often implies a type of removal and generality that is opposed to the immediacy of more tangible—literally “touchable”— things. The other options all are related to being definite in a way opposed to being abstract.

All of these words pertain to being dark or, at least, not light. The difference between “pitch-black” and the rest is the fact that it indicates the state of being completely dark. It is derived from “pitch,” which does not mean “to throw” (as it does in some situations) but instead indicates a kind of black, tarry material. “Pitch-black” merely means “as black as pitch,” indicated that something is completely black. All of the other words pertain to “dusky” sorts of light. The word “crepuscular” is likely the one word that you do not know. It merely means “related to twilight,” and could be used to describe twilight-like light.