pavilion n.

early 13c., paviloun, "large, stately tent raised on posts and used as a movable habitation," from Old French paveillon "large tent; butterfly" (12c.), from Latin papilionem (nominative papilio) "butterfly, moth," in Medieval Latin "tent" (see papillon); the type of tent was so called on its resemblance to wings. Meaning "open building in a park, etc., used for shelter or entertainment" is attested from 1680s. Sense of "small or moderate-sized building, isolated but dependent on a larger or principal building" (as in a hospital) is by 1858.