Idioms are phrases which cannot be understood simply by looking at the meaning of the individual words in the phrase.
Idiom:
not let (someone) catch you (doing something)
Meaning:
to not let someone discover you doing something
Example:
"Do not let me catch you doing that again or you will be in trouble," said the mother to her child.
List of common idioms, their meanings and examples of their usage in sentences
An expression in the usage of a language that is peculiar to itself either in having a meaning that cannot be derived from the conjoined meanings of its elements or in its grammatically atypical use of words.