timber vs two-by-four

timber and two-by-four both are nouns.

Word	Noun	Adjective	Verb	Adverb
timber	Yes	No	No	No
two-by-four	Yes	No	No	No

As nouns, two-by-four is a hyponym of timber; that is, two-by-four is a word with a more specific, narrower meaning than timber:

timber: a beam made of wood
two-by-four: a timber measuring (slightly under) 2 inches by 4 inches in cross section

Other hyponyms of timber include coulisse, sternpost, stringer.

timber (noun)	two-by-four (noun)
a beam made of wood	a timber measuring (slightly under) 2 inches by 4 inches in cross section
a post made of wood
(music) the distinctive property of a complex sound (a voice or noise or musical sound)
land that is covered with trees and shrubs
the wood of trees cut and prepared for use as building material