Vain son I ordered to get occupation (8)
I believe the answer is:
invasion
'occupation' is the definition.
(I've seen this before)
'vain son i ordered' is the wordplay.
'ordered' indicates an anagram.
'vain'+'son'+'i'='vainsoni'
'vainsoni' anagrammed gives 'INVASION'.
'to get' is the link.
(Other definitions for invasion that I've seen before include "Hostile incursion" , "Entry by force by an army" , "Unwelcome intrusion" , "Encroachment by enemy" , "Unwelcome encroachment on another country" .)