Which term is used for an action that causes distress or nervousness?

The term "unnerving" is appropriately used to describe an action or situation that causes distress or nervousness. This word conveys a sense of discomfort or anxiety, implying that something is unsettling enough to disrupt one's peace of mind. For example, an unnerving experience might leave a person feeling anxious or on edge, highlighting its effect on emotional state.

The other terms do not convey this meaning. "Uplifting" refers to something that boosts spirits or provides encouragement, which is the opposite of causing distress. "Harmonious" suggests a sense of balance and agreement, often used in contexts related to music or relationships, indicating nothing that would induce nervousness. Lastly, "reassuring" refers to actions or words that provide comfort or reassurance, effectively alleviating distress rather than causing it. Thus, "unnerving" stands out as the correct choice for describing an action that provokes unease.