Used to express complete confidence or agreement; without doubt or reservation.
From Middle English 'certeinly', derived from Old French 'certain' meaning 'sure, reliable'. The word entered English in the 13th century, combining the Latin 'certus' (determined, resolved) with the suffix '-ly' to create an adverb of absolute assurance.
Interestingly, 'certainly' has become one of the most polite ways to say 'yes' in English, often used in formal situations to show both agreement and respect. Unlike its synonym 'definitely', which can sound more casual or emphatic, 'certainly' maintains an air of dignified confidence that makes it perfect for professional settings.
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