limping iamb vs iambic trimeter

limping iamb and iambic trimeter both are nouns.

Word	Noun	Adjective	Verb	Adverb
limping iamb	Yes	No	No	No
iambic trimeter	Yes	No	No	No

As nouns, iambic trimeter is a hypernym of limping iamb; that is, iambic trimeter is a word with a broader meaning than limping iamb:

limping iamb: an iambic verse in which the last foot is a spondee or trochee instead of an iambus.
iambic trimeter: a meter of poetry consisting of three iambic units per line.

limping iamb (noun)	iambic trimeter (noun)
an iambic verse in which the last foot is a spondee or trochee instead of an iambus.	a meter of poetry consisting of three iambic units per line.