tough nut

Cardiff, on the other hand, have leapt up the table in recent weeks and will prove a tough nut to crack.

Dave is a tough nut to crack, no matter what anyone thinks they know.

"Until they do that, the trade pillar will be a tough nut to crack."

Adam Cole, the chief currency strategist at RBC, says he is biased toward a stronger dollar but admits the prevailing foreign exchange view in markets remains a tough nut to crack.

There are many other types of oaks to love, and telling them apart can be a tough nut to crack.