'To nail an assertion' definitions:

Definition of 'To nail an assertion'

From: GCIDE

Nail \Nail\, v. t. [imp. & p. p. Nailed (n[=a]ld); p. pr. & vb. n. Nailing.] [AS. naeglian. See Nail, n.]
1. To fasten with a nail or nails; to close up or secure by means of nails; as, to nail boards to the beams. [1913 Webster]
He is now dead, and nailed in his chest. --Chaucer. [1913 Webster]
2. To stud or boss with nails, or as with nails. [1913 Webster]
The rivets of your arms were nailed with gold. --Dryden. [1913 Webster]
3. To fasten, as with a nail; to bind or hold, as to a bargain or to acquiescence in an argument or assertion; hence, to catch; to trap. [1913 Webster]
When they came to talk of places in town, you saw at once how I nailed them. --Goldsmith. [1913 Webster]
4. To spike, as a cannon. [Obs.] --Crabb. [1913 Webster]
To nail an assertion or To nail a lie, etc., to detect and expose it, so as to put a stop to its currency; -- an expression probably derived from the former practice of shopkeepers, who were accustomed to nail bad or counterfeit pieces of money to the counter. [1913 Webster]