Stick with former head of economics (5)
I believe the answer is:
paste
'stick' is the definition.
(I've seen this before)
'with former head of economics' is the wordplay.
'with' says to put letters next to each other.
'former' becomes 'past' ('past' can be similar in meaning to 'former').
'head of' suggests taking the first letters.
The first letter of 'economics' is 'e'.
'past' put next to 'e' is 'PASTE'.
(Other definitions for paste that I've seen before include "Dough - adhesive - gem substitute" , "It may be put on teeth" , "Pulped meat; adhesive" , "Imitation gems; adhesive" , "Adhesive of mixed water and flour" .)