idea

not have the faintest (idea)

to have no knowledge of or no information about something. 'Do you know where Anna is? ' 'I haven't the faintest.' I haven't the faintest idea what you're talking about. (often + question word)

See also: faint

not have the foggiest (idea/notion) (informal)

to not know the answer to a question. 'Do you know where Kate's gone?' 'I haven't the foggiest.' The photocopier's broken down again, and nobody has the foggiest idea how to fix it. (often + question word)

See also: foggy

put ideas into someone's head

to make someone want to do something they had not thought about doing before, especially something stupid. Don't go putting ideas into his head. We haven't got the money for a car. (often in continuous tenses) Who put all these ideas into her head about becoming an actress?

See also: head

What's the big idea? (informal)

something that you say when you want to know why someone has done something that annoys you. What's the big idea? That's my lunch you're eating.

See also: big

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float an idea

to suggest something informally to see if people accept it or are interested in it. The mayor originally floated the idea, and it was quickly taken up by a number of city agencies.

test the waters

See also: float

not have the faintest idea

to not know anything at all about something. I didn't have the faintest idea where I was or which way I was going – I simply knew I had to get away. These people don't have the foggiest idea what America's really like.

Usage notes: also used in the forms I have no idea and I haven't the slightest idea

Etymology: perhaps based on (= I do not know) (= I don't know anything at all about something)

See also: faint