Second working satellite (4)
I believe the answer is:
moon
'satellite' is the definition.
(I know that moon is a type of satellite)
'second working' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'working' becomes 'on' (e.g. a machine is working or on).
'mo'+'on'='MOON'
(Other definitions for moon that I've seen before include "Daydream - Europa of Jupiter, say" , "Expose one's buttocks" , "Idle (around) - satellite" , "Heavenly body < exemplified in Titania?" , "The Earth's natural satellite" .)