Hello and welcome!
Our idiom this week is a hard (tough) nut to crack.
The Idioms.com tells us this phrase means:
a problem that is difficult to solve
a person that is difficult to deal with
someone or something that is difficult to understand or
a person hard to get to know or to get close to
This expression is a metaphor alluding to the tough exterior of a nutshell and how hard they are to crack open. It has been in use since the 1700s.
Have you ever used this expression?