Basic covering zips up (4)
I believe the answer is:
lino
'basic' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'covering zips up' is the wordplay.
'covering' becomes 'on'.
'zips' becomes 'il' (I can't justify this - if you can you should give a lot more credence to this answer).
'up' is a reversal indicator (in down clue: letters go upwards).
'on'+'il'='onil'
'onil' reversed gives 'LINO'.
Can you help me to learn more?
(Other definitions for lino that I've seen before include "'Floor covering, in short (4)'" , "Tough floor covering" , "Floor covering (abbr)" , "put this down?" .)