Keep shower curtains outside for event (6)
I believe the answer is:
retain
'keep' is the definition.
(synonyms)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for retain that I've seen before include "'Hold, keep back (6)'" , "Hold onto" , "Not relinquish" , "Keep in Tirane" , "Save" .)