A compound adjective consists of two adjectives placed together, often hyphenated, and modifies a noun. It can describe singular or plural nouns and typically precedes the noun it is modifying.
The statement that best describes a defining feature of a compound adjective is: a) It consists of two adjectives placed together. Compound adjectives are used to modify nouns and are often connected with a hyphen when they come before a noun. They deliver a combined quality to the noun they describe. For example, in the phrase 'well-known author,' 'well-known' is a compound adjective modifying the noun 'author.' It is the combination of 'well' and 'known,' and it clearly describes the author's notoriety.
In contrast, compound adjectives can modify singular or plural nouns and can actually precede the noun they modify, which eliminates the other options provided as incorrect definitions of a compound adjective.
So, compound adjectives enhance descriptions by merging two words to express a singular attribute of the noun, such as 'full-time job' or 'cold-blooded animal.'