Some words that describe space are:vastvoidcryptic
Not always. Sometimes idioms are just phrases.
There are 25 idioms for police. Some of these are a steal, cat burglar, on the case and on the lam.
Try this question for examples of idioms.
If you are not familiar with idioms, I would not try to specifically write a letter using them. If this is an assignment of some sort, you need to look up some common idioms and think of ways to use them in conversation so you can write a letter.
There are many idioms and phrases for 'on the back burner'. Some idioms and phrases for 'on the back burner' include 'pushing aside' and 'procrastinating'.
"Idioms for Being Afraid", "Idioms for Being Angry", "Idioms for Being Happy" are some examples of idioms found in the book "Found" by Margaret Peterson Haddix.
Here is a link to some idioms. You can pick the "non-common" ones for yourself -- some people have heard certain idioms a lot and others have not heard the same ones, so you'll need to decide that part.
Some websites that have idioms written in them include The Free Dictionary, Cambridge Dictionary, and Phrases.com. These sites provide definitions and examples of idioms to help users understand their meanings and usage in context.
The best place is to go on your search engine and type in "list idioms" You can also look at this question for some examples.
Nostalogic
cry unclemonkey's uncle
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In a pickle
There aren't any that I know of.
confererats