Army chap trained as chemist (8)
I believe the answer is:
pharmacy
'chemist' is the definition.
(thesaurus)
'army chap trained' is the wordplay.
'trained' indicates anagramming the letters (to train can mean to grow something into a shape).
'army'+'chap'='armychap'
'armychap' anagrammed gives 'PHARMACY'.
'as' acts as a link.
(Other definitions for pharmacy that I've seen before include "A chemist's shop where prescriptions are dispensed" , "Business" , "Science of dispensing drugs" , "Dispensary" , "Drug store" .)