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AS flat as a pancake ?

as old as the hills

as hard as iron

as good as gold

as green as grass

as warm as toast
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Simply write "very" + the adjective.

Very flat.
Very old.
etc.
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I'm guessing here that you are asking what these commonly heard phrases mean. The writer, in these examples, assumes that the reader, knows what a pancake is, what hills are, iron, grass, and toast. And he/she uses these objects with a descriptive term (flat, old, hard, good, green, warm) that is naturally associated with them, in order to illustrate a quality about something else that is like them. "That moth-eaten coat he's wearing is as old as the hills."

There's a lot more of them that are common, which I'm sure EnglishForward readers can offer up, for the fun of it. One which I never quite understood: "As easy as pie." I don't know if that means as easy as baking a pie, or as easy as eating one. For me eating it is a lot easier than baking it.
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Comments  
Additionally, these are all clichéd similes, which are good as gold for verbal communication, but which should be avoided like the plague in formal writing.
Students: Are you brave enough to let our tutors analyse your pronunciation?
For sure, MrM.

How about: "avoid it like the plague"? I bet you know a thousand of them.

I'd like to hear George Carlin do a stand-up monologue using nothing but cliched similes
very well ! thank you again for your understandingEmotion: smile