One second inside current record (4)
I believe the answer is:
disc
'record' is the definition.
(eg a CD, compact disc)
'one second inside current' is the wordplay.
'one' becomes 'i' (Roman numeral).
'second' becomes 's' (common abbreviation).
'inside' means one lot of letters goes inside another.
'current' becomes 'DC' (abbreviation for direct current).
'i'+'s'='is'
'is' inserted within 'dc' is 'DISC'.
(Other definitions for disc that I've seen before include "Flat, circular plate - record" , "Body without limbs" , "Flat thin round object" , "jockey may be after" , "'Round, flat shape (4)'" .)