Picture a very long table with only five or six chairs at it, and a large crowd standing outside the door. Everything that matters is decided at that table, and the door does not open. A useful way to hold this word is the gap between how few chairs there are and how many people have to live with what is decided on them.
From the word’s history
The packet gives the word as Greek oligos, few, plus arkhe, rule, reaching English through Late Latin and French, and notes the surface analysis oligo- plus -archy. The few and the ruling are both written into the word.
證據裡寫得很清楚：來自希臘文 olígos（少數）加 arkhḗ（統治），經 Late Latin 和法文進入英文；表面上也可以拆成 oligo- 加 -archy。「少數」和「統治」兩塊都直接寫在字裡面。學會這兩塊，意思幾乎不用背。
Wiktionary (kaikki extract) via evidence packet: oligarchy, etymology_text (Greek oligos + arkhe; surface analysis oligo- + -archy)
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