Norse messenger goddess Gná : etymology?

From: Joao S. Lopes
Message: 67150
Date: 2011-01-28

What's the meaning of ON Gna: , a messenger goddess, similar to Iris?
Snorri links Gna: to gnaefir, what would imply a proto-form *Gnai(h)wo:(n) or
*Gnae:(h)wo:(n).
Was G- a preffix ?

JS Lopes