One covering row about Liberal (5)
I believe the answer is:
tiler
'one covering' is the definition.
The definition suggests a singular noun which matches the answer.
'row about liberal' is the wordplay.
'row' becomes 'tier' (a tier is a row of things).
'about' means one lot of letters goes inside another.
'liberal' becomes 'l' (abbreviation).
'tier' going around 'l' is 'TILER'.
Can you help me to learn more?
(Other definitions for tiler that I've seen before include "Masons' doorkeeper" , "Workman who fixes glazed rectangles in bathrooms" , "Worker who lays small squares" , "Roof worker" , "High-level operator" .)