G-series agent vs GD

G-series agent and GD both are nouns.

Word	Noun	Adjective	Verb	Adverb
G-series agent	Yes	No	No	No
GD	Yes	No	No	No

As nouns, GD is a hyponym of G-series agent; that is, GD is a word with a more specific, narrower meaning than G-series agent:

G-series agent: a non-persistent nerve agent discovered and synthesized during or prior to World War II by Dr. Gerhard Schrader.
GD: a nerve agent easily absorbed into the body; a lethal cholinesterase inhibitor that is highly toxic when inhaled

Other hyponyms of G-series agent include GB, sarin, soman, GA, tabun.

G-series agent (noun)	GD (noun)
a non-persistent nerve agent discovered and synthesized during or prior to World War II by Dr. Gerhard Schrader.	a nerve agent easily absorbed into the body; a lethal cholinesterase inhibitor that is highly toxic when inhaled