Think of a wall coming down: broken stone, an open roof, a shape you can still recognise but can no longer use. Ruinous keeps that picture of collapse. Sometimes the word sits on the thing that has already fallen. Sometimes it sits on the force strong enough to bring something else down. What collapses may be a building, a business, or the money a family had put aside.
From the word’s history
The supplied source traces ruinous through Middle English ruynous and Old French ruinos to Latin ruinosus, and analyses it on the surface as ruin + -ous.
來源把 ruinous 追到中古英語 ruynous、古法語 ruinos，再回到拉丁文 ruīnōsus；表面上拆開來就是 ruin（毀壞、廢墟）加上 -ous（帶有…性質的）。字面意思是「帶著崩塌性質的」，這正好對上今天三個用法共有的那個倒下來的畫面。
Wiktionary entry for 'ruinous' as supplied in this batch's evidence packet (source_ref kaikki:3f6f69a190036ae4:901894312)
登入就可以看每一支怎麼連回核心畫面。