交集
jiāo jí · HSK 7
intersection (symbol ∩) (set theory)
🔗 交 (cross/intersect) + 集 (set/gather) = the set where two sets cross — intersection ∩
交 carries the sense of crossing or meeting; 集 means a gathering or, in math, a set. Together 交集 names the elements two sets share — what overlaps when they cross. Contrast with 并集 (union ∪), which gathers everything from both.
交 — top 亠 + 父-like crossed legs
Originally a pictograph of a person standing with legs crossed, showing the idea of crossing or intersecting. From this concrete image, the meaning extended to abstract senses like 'exchange,' 'interact,' and 'hand over.' Modern uses such as 交流 (exchange) and 交通 (traffic) all trace back to this core notion of crossing.
集 — bird 隹 on top of tree 木
集 is an ideograph showing a bird (隹) perched on a tree (木). The original form depicted three birds gathering on a tree, later simplified to one. From 'birds flocking together' it extended to mean 'gather, collect, assemble,' and by extension 'collection' or 'volume' of writings.