同い年
おないどし · onaidoshi · JLPT N1 · noun
age
同 — 冂 enclosure + 一 + 口 mouth
Originally depicted multiple mouths gathered under one cover or enclosure, suggesting people speaking together in agreement. From this image of voices joining, it came to mean 'same,' 'together,' or 'alike.' The shared cover symbolizes unity.
年 — grain 禾 over person 人 (oracle bone)
Originally a pictograph of a person carrying a bundle of harvested grain on their back, representing the yearly grain harvest. Because harvests came once a year, the character shifted from meaning 'harvest' to meaning 'year.' The modern form 年 obscures the original 禾 (grain) + 人 (person) structure.