a person who eats elevenses, a mid-morning meal or snack, especially common in British English.
From elevenses (the meal time) plus -er (one who does something). Elevenses comes from 'eleven o'clock' where this snack is traditionally eaten.
Eleveners are British people who stick to the tradition of taking a tea break and biscuit around 11 AM—it's practically a cultural institution in the UK, as important as lunch or dinner.
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