Chap finds a trainee regal (5)
I believe the answer is:
royal
'regal' is the definition.
(I know that regal can be written as royal)
'chap finds a trainee' is the wordplay.
'chap' becomes 'roy' ().
'finds' means one lot of letters go next to another.
'trainee' becomes 'l' (as in an L-plate for a learner driver).
'roy'+'a'+'l'='ROYAL'
(Other definitions for royal that I've seen before include "First-rate" , "Befitting a monarch" , "complete" , "Relating to a sovereign" , "Sort of jelly, flush or blue" .)