timber line vs timberline

timber line and timberline both are nouns.

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

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

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

Other synonyms of timber line include tree line.

timber line (noun)	timberline (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