osso duro de roer

Portuguese

Etymology

Literally, “hard bone to gnaw”.

Noun

osso duro de roer m (plural ossos duros de roer, metaphonic)

1. (idiomatic) hard nut to crack (problem that is challenging to solve)
2. (idiomatic) hard nut to crack (situation, person, group, etc. which is difficult to overcome or deal with)
3. (idiomatic) a brave or hardy person or organisation