One card bearing any number of spots (4)
I believe the answer is:
acne
'spots' is the definition.
(skin condition causing spots)
'one card bearing any number' is the wordplay.
'one card' becomes 'ace' (ace is a type of playing card).
'bearing' indicates putting letters inside.
'any number' becomes 'n' (mathematical symbol for an unspecified number).
'ace' going around 'n' is 'ACNE'.
'of' acts as a link.
(Other definitions for acne that I've seen before include "Pimply ailment of adolescnce" , "Inflammation of glands in skin" , "(Inflammation causing) spots" , "Skin problem, mainly of teenagers" , "Skin condition prevalent among teenagers" .)