What is the single most defining anatomical feature of a true finch?

Answer

A stout, deep, conical bill

The text specifies that the stout, deep, conical bill, wide at the base and tapering to a sharp point, is perhaps the single most defining feature of the Fringillidae family, adapted for crushing hard seed hulls.

What is the single most defining anatomical feature of a true finch?
birdanimaldescriptionfinch