It was a tremendously reassuring feeling to know I had their full support.

reassuring 是由动词 reassure（使安心、使放心）加上后缀 -ing 构成的形容词。reassure 由前缀 re-（表示"再次"）和 assure（保证、使确信）组成，字面意思是"再次保证"。 reassuring 表示"令人安心的、使人放心的"，描述能消除他人疑虑或担忧的事物。