Train to become head of economics (5)
I believe the answer is:
suite
'train' is the definition.
(I've seen this before)
'become head of economics' is the wordplay.
'become' becomes 'suit' ('suit' can be a synonym of 'become').
'head of' suggests taking the first letters.
The first letter of 'economics' is 'e'.
'suit'+'e'='SUITE'
'to' acts as a link.
(Other definitions for suite that I've seen before include "Musical composition" , "Train; set of rooms" , "Three-piece - -" , "Set, e.g. of furniture" , "Collection of pieces" .)