Art (5)
'art' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for skill that I've seen before include "Aptitude" , "Ability acquired by training" , "Expertise; art" , "Expertise, dexterity" , "Ability - dexterity" .)
(Other definitions for deco that I've seen before include "Art's partner" , "Style of design popular in the 1920s and 1930s" , "Art -, C 20 style of ornamentation" .)