timberline vs timber line

timberline and timber line both are nouns.

Word	Noun	Adjective	Verb	Adverb
timberline	Yes	No	No	No
timber line	Yes	No	No	No

As nouns, timberline and timber line are synonyms defined as:

timberline and timber line: line marking the upper limit of tree growth in mountains or northern latitudes

Other synonyms of timberline include tree line.

timberline (noun)	timber line (noun)
line marking the upper limit of tree growth in mountains or northern latitudes	line marking the upper limit of tree growth in mountains or northern latitudes