Unobtrusive, a. — Webster enters it under “unobtrusive”
Not obtrusive; not presuming; modest. -- Un`ob*tru"sive*ly, adv. -- Un`ob*tru"sive*ness, n.
Shades of meaning
Fernald has no entry of its own for unobtrusiveness; he lists it under modesty.
He lists it without comment; the entries above explain its neighbors.