芥蒂 (pronounced jiè dì, not gài) is a literary noun referring to a small obstruction or resentment in one's heart — a grudge, a lingering ill feeling, or a barrier in a relationship. It's often used in negative constructions like 没有芥蒂 ('have no hard feelings') or with verbs like 消除 ('eliminate') to describe mending a rift. The word is metaphorical, coming from the literal meaning of a tiny stem or thorn that gets stuck.