Cool MateNo idea vs Not sure
When to use each in English, with meaning, register, and examples.
No idea
InformalTop 2,000 (common)
Not sure
| No idea | Not sure | |
|---|---|---|
| Pronunciation | 🇬🇧 //nəʊ aɪˈdɪə//🇺🇸 //noʊ aɪˈdiə// | |
| Meaning | I don't know or understand | |
| Example | I have no idea where my keys are. | - |
| Register | Informal | - |
| How common | Top 2,000 (common) | - |
| Collocations | have no idea, give no idea, no idea what's going on | - |
| Antonyms | have a clue, know, be certain, understand | - |
| Common mistakes | Using it in a formal context where a more serious phrase is needed., Confusing it with 'no clue', which has a similar meaning. | - |
| Usage notes | Use in casual conversations when you have no knowledge of something. Avoid in formal situations. | - |
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Frequently asked questions: No idea vs Not sure
What's the difference between No idea and Not sure?
No idea: I don't know or understand Not sure:
Can I use No idea and Not sure interchangeably?
Not always. No idea and Not sure are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.