chasteness(n = noun.attribute) restraint, simpleness, simplicity - lack of ornamentation; "the room was simply decorated with great restraint"
is a kind of plainness
Derived form adjective chaste₂

1.  Chastity; purity. [1913 Webster]

2.  Freedom from all that is meretricious, gaudy, or affected; as, chasteness of design. [1913 Webster]