A person who disciplines or enforces discipline; someone who trains or punishes others to maintain order or control.
From discipline + -er (suffix forming agent nouns indicating a person who performs an action). This follows the standard English pattern of adding -er to verbs to create agent nouns, though it's not commonly used compared to 'disciplinarian.'
A 'disciplinarian' sounds more official and established—think of a strict teacher—while a 'discipliner' sounds more like someone actively in the moment enforcing rules, yet English speakers have mostly chosen the former word over this one.
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