One second ago, within, laid on thick (7)
I believe the answer is:
impasto
'laid on thick' is the definition.
The definition suggests a singular noun which matches the answer.
'one second ago within' is the wordplay.
'one' becomes 'i' (Roman numeral).
'second' becomes 'mo' (both are short periods of time).
'ago' becomes 'past' (similar in meaning).
'within' means one lot of letters goes inside another.
'mo' enclosing 'past' is 'mpasto'.
'i'+'mpasto'='IMPASTO'
Can you help me to learn more?
(Other definitions for impasto that I've seen before include "artistic technique" , "application of paint in this way" , "Thickly-applied painting technique" , "Sort of paint" , "artist's application" .)