Of a thing: unpretentious or moderate in size, appearance, style, etc.; (of a sum of money or financial means) limited, not lavish or extensive…

Humble in rank, condition, or quality; insignificant, unimportant. Also in weakened sense: unexceptional, ordinary.

Of a building, etc.: unostentatious, plain. Obsolete.

Characterized or accompanied by modesty.

Not ambitious or aspiring; devoid of ambition. Of thoughts, occupations, productions, etc.

Free from excess; not extreme; moderate, modest; restrained; understated; (also of colour) muted, subdued.

figurative. Chastened, modest, restrained from all excess. of tastes, qualities, etc.

Free from assumption; unpretentious. Of things.

(un-, prefix1 affix 1.)

(a) having or using a low musical key; (b) = low key, adj. 2.

Art and Photography. Of a picture or lighting: dim or dull in tone.