Exercise in trade somehow got thinner (7)
I believe the answer is:
tapered
'got thinner' is the definition.
The definition and answer can be both related to change as well as being past participle verbs.
Maybe there's an association between them I don't understand?
'exercise in trade somehow' is the wordplay.
'exercise' becomes 'pe' (Physical Education).
'in' means one lot of letters goes inside another.
'somehow' indicates an anagram.
'trade' with letters rearranged gives 'tared'.
'pe' placed within 'tared' is 'TAPERED'.
Can you help me to learn more?
(Other definitions for tapered that I've seen before include "Becoming narrower towards one end" , "came to the point" , "With thickness reduced towards an end" , "Coming to a point" , "Gradually narrowing" .)