介入
jièrù · HSK 7
intervene
🚪 介 = go-between + 入 = enter; intervene = enter into the middle of things
介 carries the sense of an intermediary or being between two sides, and 入 means to enter. Stack them and you get the act of entering into a situation between others, which is exactly to intervene or get involved.
入 — single pictograph, two slanting strokes
入 is a pictograph showing an arrowhead or pointed entrance, with two strokes converging downward to suggest something going inward. The original sense was 'to enter,' and it still carries that meaning today. It contrasts visually with 人 (person), where the strokes cross differently at the top.