Which term refers to causing someone to lose their composure?

The term that refers to causing someone to lose their composure is "discomfit." This word originates from the Old French "desconfit," which means to defeat or to make uneasy. In contemporary usage, discomfit means to make someone feel uneasy, confused, or embarrassed, thereby disrupting their calmness or confidence. This aligns perfectly with the notion of losing one's composure, as it suggests a state of discomfort or disarray.

The other options do not convey the same meaning. "Comfort" pertains to providing relief or consolation, which is the opposite of unsettling someone. "Stabilize" suggests making something steady or secure, and does not imply any disruption to composure. "Encourage" refers to providing support or confidence to someone, promoting composure rather than undermining it. Thus, "discomfit" is the most appropriate choice as it specifically denotes the act of creating a loss of composure in someone.