Mars socialist idea over case for employment (3,6)
I believe the answer is:
red planet
'mars' is the definition.
(synonyms)
'socialist idea over case for employment' is the wordplay.
'socialist' becomes 'red' (socialism is often associated with the colour red).
'idea' becomes 'plan' (plan is a kind of idea).
'over' means one lot of letters go next to another.
'case for' says to hollow out the word (remove centre letters) (the letters which encase the others are used).
'employment' with its middle removed is 'et'.
'red'+'plan'+'et'='RED PLANET'
(Other definitions for red planet that I've seen before include "one of our neighbours" , "object in 21 [SPACE]" , "Colourful description of Mars" , "Informal name for Mars" , "celestial body" .)