The word "芥蒂" is formed by combining the character "芥", which originally means mustard or a small grass, often implying something minor or trivial, with "蒂", which refers to the stem or base of a fruit, symbolizing a root or cause. Together, they create a compound word where the smallness of "芥" and the foundational aspect of "蒂" metaphorically represent a slight or grievance that becomes the entrenched root of lasting resentment or a grudge.