trench vs ditch

trench and ditch both are nouns.

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

As nouns, ditch is a hypernym of trench; that is, ditch is a word with a broader meaning than trench:

trench: a ditch dug as a fortification having a parapet of the excavated earth
ditch: a long narrow excavation in the earth

As nouns, ditch is a hypernym of trench; that is, ditch is a word with a broader meaning than trench:

As verbs, trench and ditch are synonyms defined as:

trench (noun)	ditch (noun)
a ditch dug as a fortification having a parapet of the excavated earth	a long narrow excavation in the earth
any long ditch cut in the ground	any small natural waterway
a long steep-sided depression in the ocean floor

trench (verb)	ditch (verb)
cut or carve deeply into	crash or crash-land
dig a trench or trenches	cut a trench in, as for drainage
cut a trench in, as for drainage	make an emergency landing on water
fortify by surrounding with trenches	forsake
set, plant, or bury in a trench	throw away
impinge or infringe upon	sever all ties with, usually unceremoniously or irresponsibly