ration vs field ration

ration and field ration both are nouns.

Word	Noun	Adjective	Verb	Adverb
ration	Yes	No	Yes	No
field ration	Yes	No	No	No

As nouns, field ration is a hyponym of ration; that is, field ration is a word with a more specific, narrower meaning than ration:

ration (noun)	field ration (noun)
the food allowance for one day (especially for service personnel)	rations issued for United States troops in the field
a fixed portion that is allotted (especially in times of scarcity)

ration (verb)	field ration (verb)
distribute in rations, as in the army
restrict the consumption of a relatively scarce commodity, as during war