"in the open air, out of the house," 1817, from outdoor + adverbial genitive -s. As a noun, "open spaces," it is recorded from 1857; the great outdoors is recorded by 1932. Out a doors (adv.) is from 1520s.
Entries linking to outdoors
outdoor adj.
"that is done or used in the open air, not in the house," 1748, from out- + door. Out-of-door is from c. 1800.
outdoorsman n.
"one who enjoys outdoors activities," 1924, American English, from outdoors + man (n.).