He always spoke to them very respectfully.

respectfully 是形容词 respectful（恭敬的）加上后缀 -ly 构成的副词形式，表示"以恭敬的方式"。respectful 由名词 respect（尊敬）加上形容词后缀 -ful（充满...的）构成，字面意思是"充满尊敬的"。