こないだ

Colloquial contraction of この間(あいだ) (the other day). Very common in casual spoken Japanese.

Common patterns

• こないだの～: the ~ from the other day
• こないだは～: regarding the other day (used to thank or apologize for something recent)
• こないだから: since the other day

Formality levels

• こないだ: casual (conversation only)
• この間(あいだ): neutral (spoken and written)
• 先日(せんじつ): formal (business, letters, polite speech)

Usage

Refers to a vague recent past — anywhere from a few days to a few weeks ago. Not appropriate for formal writing or business contexts. Often used as an opener: こないだね… (You know, the other day…).