Frequency: The word is one of the 700 most common words in English.
A ~ is a situation that is unsatisfactory and causes difficulties for people.
...the economic ~s of the inner city...
The main ~ is unemployment...
He told Americans that solving the energy ~ was very important...
N-COUNT: usu with supp, oft N of/with n
A ~ is a puzzle that requires logical thought or mathematics to solve it.
With mathematical ~s, you can save time by approximating.
Problem children or ~ families have serious ~s or cause serious ~s for other people.
In some cases a ~ child is placed in a special school...
ADJ: ADJ n