共通
きょうつう · kyoutsuu · JLPT N3 · na-adj
mutual
共通 = together (共) + pass through (通): what runs through everyone
共 means shared or together, as in 共有 (to share). 通 means to pass through or go through, as in 交通 (traffic). Something 共通 runs through all parties alike, so it means common or mutual, as in 共通点 (point in common).
共 — 两手 (廾) holding up an object
共 originally depicted two hands raised together, lifting or offering something jointly. The ancient form showed a vessel or object held up by paired hands, conveying shared action. From 'lifting together' it shifted to mean 'together,' 'common,' or 'share.'
通 — 辵 (辶) walk + 甬 yǒng (phonetic)
通 is a semantic-phonetic compound. The 辶 (chuò) component means 'walk' or 'movement', giving the meaning of going through or passing. 甬 (yǒng), originally depicting a hanging bell or a path, supplies the sound. Together they convey 'to pass through, communicate, connect'.