Final answer:
In the context of the question, 'euphemism' refers to a gentler or less direct alternative for a word or phrase that might be unpleasant or harsh; therefore, it is closely related to a nickname, which serves a similar purpose.
Step-by-step explanation:
The term euphemism is used to describe a mild or indirect word or expression that is used in place of one that may be considered too harsh or blunt, especially when referring to something unpleasant or embarrassing. Based on this definition, in line 5, the word euphemism refers to a nickname (C), which is a term often used to avoid using a more direct or potentially offensive term.