пядь

noun, feminine, inanimate

Very rarely used word (top 30,000)

Translation

Необязательно быть семи пяде́й во лбу, чтобы знать, кто э́то сказа́л.You don't have to be a genius to know who said that.
Не надо быть семи пяде́й во лбу, чтобы э́то поня́ть.You don't need to be a rocket scientist to figure that out.

Note: Stress change.