Thanks, Brian. I wondered what the derivation was.
Grace
I've not had time to look at the translations, but I can
help out here: you want Zoëga s.v. <gerzkr>. (Modern
Icelandic has done away with <z>.) The Old Norse spelling
of the byname is <(h)inn gerzki>, <gerzki> being the masc.
nom. sing. in the weak adjective declension. The word
properly means 'of or from Garðar'; <Garðar> 'strongholds',
the plural of <garðr>, referred to the old
Scandinavian-Russian kingdom around what is now Novgorod.
(Another name for it was <Garðaríki>, literally 'kingdom of
castles, kingdom of strongholds'.