underdress

(ŭnˈdər-drĕsˌ)

1. Apparel worn beneath outer garments; underclothing.
2. An outer garment, such as a dress beneath a tunic or coat, that is worn as part of a costume or suit.

1. To dress too informally for the occasion.
2. To dress without sufficient warmth: You're underdressing that baby for such a cold day.