Encourage chief to be a boffin (7)
I believe the answer is:
egghead
'a boffin' is the definition.
(I've seen this before)
'encourage chief' is the wordplay.
'encourage' becomes 'egg'.
'chief' becomes 'head' (synonyms).
'egg'+'head'='EGGHEAD'
'to be' acts as a link.
(Other definitions for egghead that I've seen before include "where soldiers may take a dip?" , "Brainy type" , "Intellectual person" , "Intellectual (sl.)" , "may take a bashing at the breakfast table" .)