Which of the following describes someone who is very irritable?

The term "splenetic" accurately describes someone who is very irritable. Originating from the historical belief that the spleen was responsible for producing a melancholic temperament, "splenetic" has evolved to refer specifically to individuals characterized by ill temper and irritability. This word encompasses a sense of chronic annoyance or bad humor, making it fitting for someone prone to irritability.

In contrast, "stentorian" refers to a loud and powerful voice—often used to describe someone who speaks with great volume rather than irritable disposition. "Sophomoric" typically describes someone who is juvenile or immature, particularly in their judgment. "Runic" pertains to the ancient written characters of Germanic languages and has no relevance to personality traits related to irritability. Therefore, the word "splenetic" stands out as the most suitable descriptor for someone who is very irritable.