the meaning of a matter of concerned and the fell on deaf ears and a big fish in a small pond and the under the counter
A matter of concern > something about which there is worry
It is a matter of concern that the child is left alone all night.
Fell on deaf ears > No-one paid any attention
All I said to him about his behaviour fell on deaf ears.
A big fish in a small pond > Someone who is important in a small way
The local shopkeeper is a big fish in a small pond; the assistant in the big store is a small fish in a big pond.
Under the counter > clandestinely
I got these cigarettes under the counter