1660s, "pertaining to trees," from Latin arboreus "pertaining to trees," from arbor, arboris "tree" (see arbor (n.2)) + -al (1). From 1834 as "living in or among trees."
Entries linking to arboreal
arbor n.2
"main support or beam of a machine," 1650s, from Latin arbor, arboris "tree," from Proto-Italic *arthos, which de Vaan derives from PIE *herdhos "height, uprightness," from root *eredh- "to grow, high" (see ortho-).
-al 1
suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).