entries → 啊
TSUMUGU · TOCFL 1 (est.) · 字
啊 character · TOCFL 1 (est.)
啊 ＝ 口 ＋ 阿
ㄚ · ā
interjection/particle — ah!, oh!; sentence-final softener

字源 FORM — what the parts do

口義a mouth — the sound coming out
阿聲ā — gives the reading阝(mound) + 可, itself off the 可 sound series
A mouth (口) marks this as something spoken, not meant. 阿 ā carries the sound straight. The mouth (口) flags 啊 as a noise the lips make — surprise (啊，下雨了), or a soft tag hung on the end of a sentence (好啊).

故事 STORY — a scene to remember it by

嘴（口）一張，聲音先出來——「啊！」——話還沒想好。
The mouth (口) opens and the sound leads — "ah!" — before the words are ready.
字源記憶法
意 · Meanings
(本義)啊（驚嘆）— ah!, oh! — surprise or realization常用
→好啊、是啊— sentence-final softening particle常用
(本義) original meaning · → ⇒ each arrow = one more step of extension
關 · Related
呵hēthe lookalike — 呵 hangs 可 off the mouth (to scold, to laugh); 啊 hangs 阿阿āthe sound donor, standing alone — a prefix on names