also out-patient, 1715, "patient not residing at a hospital, person who is treated at a hospital but not admitted," from out- + patient (n.). The adjective is recorded by 1879.
Entries linking to outpatient
out-
in Old English a common prefix with nouns, adjectives, adverbs, and verbs, "out, outward, outer; forth, away," from out (adv.). The use was even more common in Middle English, and also with the senses "outer, outside, on the outside, from without, external, externally; apart; greatly, extremely; completely, thoroughly, to completion." Other senses of out that extended into the use as a prefix include "beyond the surface or limits; to the utmost degree; to an explicit resolution."
In composition out has either its ordinary adverbial sense, as in outcast, outcome, outlook, etc., or a prepositional force, as in outdoors, or forms transitive verbs denoting a going beyond or surpassing of the object of the verb, in doing the act expressed by the word to which it is prefixed, as in outrun, outshine, outvenom, etc. In the last use especially out may be used with almost any noun or verb. [Century Dictionary]
patient n.
"suffering, injured, or sick person under medical treatment," late 14c., from Old French pacient (n.), from the adjective, from Latin patientem "suffering" (see patience). In Middle English also of anyone who suffered patiently.