注入
zhùrù · HSK 7
to pour into
💉 注 pour + 入 enter = pour-in, i.e. inject or infuse
注 carries the sense of pouring or channeling a liquid; 入 means to enter or go in. Together the liquid is poured in, which lands on inject, infuse, mainline.
注 — water 氵 + master 主 (phonetic)
A semantic-phonetic compound: 氵 (water) gives the meaning of pouring or flowing, while 主 supplies the sound. The original sense was 'to pour water in,' which extended to 'concentrate, focus' (as in pouring attention) and 'to annotate' (pouring explanation into a text).
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.