trench vs fire trench

trench and fire trench both are nouns.

Word	Noun	Adjective	Verb	Adverb
trench	Yes	No	Yes	No
fire trench	Yes	No	No	No

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

trench: a ditch dug as a fortification having a parapet of the excavated earth
fire trench: a trench especially constructed for the delivery of small-arms fire

Other hyponyms of trench include approach trench, communication trench, fosse, moat, slit trench.

trench (noun)	fire trench (noun)
a ditch dug as a fortification having a parapet of the excavated earth	a trench especially constructed for the delivery of small-arms fire
any long ditch cut in the ground
a long steep-sided depression in the ocean floor

trench (verb)	fire trench (verb)
cut or carve deeply into
dig a trench or trenches
cut a trench in, as for drainage
fortify by surrounding with trenches
set, plant, or bury in a trench
impinge or infringe upon