当たり前
あたりまえ · atarimae · JLPT N3 · na-adj
usual
当たり (allotted, per person) + 前 (portion) = your fair share, so: only natural
Originally 当たり前 meant the share each person was due, like a worker's cut of the catch. Getting your due portion was expected, so the word moved from 'one's rightful share' to 'natural, usual, obvious'.
当 — small ⺌ + crown 冖 + hand 彐 (simplified from 當: 尚 + 田)
Originally written 當, combining 田 'field' with 尚 as a phonetic. The early sense was 'to match' or 'face' a field of equal value, extended to 'correspond to', 'ought to', and 'serve as'. The simplified form 当 streamlines the upper 尚 component.
前 — top 丷 + 一 + 月 (moon) + 刂 (knife)
Originally written 歬, depicting a foot 止 above a boat 舟, meaning to advance or go forward. Over time the form evolved and the knife radical 刂 was added, while 止 and 舟 fused into the modern shape. The core meaning 'front, before, ahead' has stayed consistent.