Thought practice is inspired by doctor (5)
I believe the answer is:
mused
'thought' is the definition.
(musing is a kind of thinking)
'practice is inspired by doctor' is the wordplay.
'practice' becomes 'use' (use is a kind of practice).
'is inspired by' means one lot of letters goes inside another (some letters breathed in or 'inspired' by others).
'doctor' becomes 'md' (synonyms).
'use' inserted into 'md' is 'MUSED'.
(Other definitions for mused that I've seen before include "Reflected or pondered" , "Fuddled" , "Closer" , "Was deep in thought" , "'Meditated, mulled (5)'" .)