These are the only words in the English language which start with "gn". You can copy this post and save it for reference if you want to.
gnomon (an old favorite of mine)
and, of course.... gnu.
Gns is the abbreviation for guineas. Bet you didn't know that. Me neither.
All the rest are simply variations of the above, abbreviations, or scientific terms that don't count. I consider Gnathostomulida and it's brethren to be scientific. Just so you know. Foreign words like gnocchi that have crept into the language don't count either. Old Norwegian words are acceptable, though.