The Collaborative International Dictionary of English v.0.48:

Ambient \Am"bi*ent\, a. [L. ambiens, p. pr. of ambire to go
   around; amb- + ire to go.]
   Encompassing on all sides; circumfused; investing. "Ambient
   air." --Milton. "Ambient clouds." --Pope.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ambient \Am"bi*ent\, n.
   Something that surrounds or invests; as, air . . . being a
   perpetual ambient. --Sir H. Wotton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ambient
    adj 1: completely enveloping; "the ambient air"; "ambient
           sound"; "the ambient temperature"

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "ambient":
   ambience, atmosphere, circling, circumambient, circumferential,
   circumflex, circumfluent, circumfluous, circumjacent, climate,
   embracing, encircling, enclosing, encompassing, enfolding,
   enveloping, environing, medium, milieu, mise-en-scene, neighboring,
   peripheral, roundabout, suburban, surrounding, surroundings,
   wrapping