Empty decor borders on curtain, dropping short (5)
I believe the answer is:
drain
'empty decor borders' is the definition.
'drain' can be an answer for 'empty' (draining is a kind of emptying). I am not certain of the 'decor borders' bit.
'on curtain dropping short' is the wordplay.
'on' is a charade indicator (letters next to each other).
'curtain' becomes 'rain' (I am not sure about this - if you are sure you should believe this answer much more).
'short' says to take the initial letters.
The initial letter of 'dropping' is 'd'.
'rain' after 'd' is 'DRAIN'.
Can you help me to learn more?
(Other definitions for drain that I've seen before include "Draw off liquid" , "Something using up resources" , "Nadir (anag.)" , "Filter" , "Exhaust - pipe" .)