One way to hold muster: bodies that were spread out are called in to one place, lined up, and looked over so somebody can count them. That is the whole picture — the calling in, and the counting at the end of it. Put soldiers in the line and you get the army meanings; put sheep in it and you get the Australian farm meanings; put a person in it and walk an inspector past, and you get pass muster. Take the line away and keep only the effort of collecting something scattered, and you get the commonest use today: mustering courage that was not all in one place to begin with.
From the word’s history
The packet's Wiktionary entry traces muster through Middle English musteren and Anglo-Norman mostrer back to Latin mōnstrō, to show. The oldest idea is display, and it explains why calling people in and counting them share one word: you brought them together in order to show them.
來源的 Wiktionary 詞條把 muster 追到中古英語 musteren、盎格魯諾曼語 mostrer，再往上是拉丁文 mōnstrō「展示」（與法文 montrer 同源）。最早的意思是「亮出來給人看」，這正好解釋了為什麼「叫攏」和「清點」會共用一個字：把人集中起來，本來就是為了讓人看過一遍。
Wiktionary entry for muster (etymology 1), supplied in this packet as kaikki:3f6f69a190036ae4:654114467 / :654140527
登入就可以看每一支怎麼連回核心畫面。