The correct word similar in meaning to "roil" is "vex". To "roil" means to disturb or agitate, often causing frustration or anxiety, which aligns with the meaning of "vex."
- Dreamy refers to something that is idealized or whimsical, not related to agitation.
- Plush refers to something luxurious, not linked to the meaning of "roil."
- Scamp refers to a mischievous person, not related to the meaning of "roil."
Thus, the correct answer is "vex".