tough nut to crack

== English == === Alternative forms === tougher nut to crack, toughest nut to crack === Pronunciation === === Noun === tough nut to crack (plural tough nuts to crack) Synonym of hard nut to crack. ==== Usage notes ==== Tough/er/est nut to crack is by far the most common form in COCA (US), about equal to hard/er/est nut to crack at BNC (UK). ==== Translations ====