The realm, condition, or dominion of dealers; the world of dealing or trading.
From dealer (one who deals) plus -dom (Old English suffix meaning 'realm' or 'condition'). Similar to kingdom or dukedom, this creates a collective noun.
The suffix -dom is wonderfully flexible—we can talk about 'dealerdom' the same way we talk about 'kingdom' or 'serfdom,' showing how English speakers have always created abstract realms out of concrete roles.
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