Source : Webster's Revised Unabridged Dictionary (1913)

Unobtrusive \Un`ob*tru"sive\, a.
   Not obtrusive; not presuming; modest. -- {Un`ob*tru"sive*ly},
   adv. -- {Un`ob*tru"sive*ness}, n.

Source : WordNet®

unobtrusive
     adj : not obtrusive or undesirably noticeable; "a quiet,
           unobtrusive life of self-denial" [syn: {unnoticeable}]
           [ant: {obtrusive}]