वास्तव में पता लगाना  =  define
The reasons why some children do badly at school are difficult to nail down.

बाध्य करना  =  force
She says she'll come, but i can't nail her down to a specific time.

कीलें जड़ कर सुरक्षित करना  =  make secure
To make a carpet,lid,etc secure with nails