trimmer joist vs joist

trimmer joist and joist both are nouns.

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

As nouns, joist is a hypernym of trimmer joist; that is, joist is a word with a broader meaning than trimmer joist:

trimmer joist: 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.
joist: beam used to support floors or roofs

trimmer joist (noun)	joist (noun)
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.	beam used to support floors or roofs