Definitions for underdressˌʌn dərˈdrɛs; ˈʌn dərˌdrɛs
Random House Webster's College Dictionary
un•der•dressˌʌn dərˈdrɛs; ˈʌn dərˌdrɛs(v.; n.; v.i.)
to clothe oneself less formally than is usual or fitting for the circumstances.
(n.)garments worn beneath others; underclothes.
a slip, petticoat, or other underskirt.
Origin of underdress:
dress without sufficient warmth
"She was underdressed for the hiking trip and suffered hypothermia"
dress down, underdress(verb)
dress informally and casually
"On Fridays, employees can underdress"
To dress in insufficiently warm clothes.
To dress in insufficiently formal clothes.