joist vs trimmer

joist and trimmer both are nouns.

Word	Noun	Adjective	Verb	Adverb
joist	Yes	No	No	No
trimmer	Yes	No	No	No

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

joist: beam used to support floors or roofs
trimmer: joist that receives the end of a header in floor or roof framing in order to leave an opening for a staircase or chimney etc.

Other hyponyms of joist include floor joist, trimmer joist.

joist (noun)	trimmer (noun)
beam used to support floors or roofs	joist that receives the end of a header in floor or roof framing in order to leave an opening for a staircase or chimney etc.
	capacitor having variable capacitance; used for making fine adjustments
	a machine that trims timber
	a worker who thins out and trims trees and shrubs