Fashionable period, going forward had to stop (9)
I believe the answer is:
terminate
'stop' is the definition.
(synonyms)
'fashionable period going forward had' is the wordplay.
I cannot quite see how this works, but
'fashionable' could be 'in' (similar in meaning) and 'in' is located in the answer.
'period' could be 'term' (term is a kind of period) and 'term' is found within the answer.
'had' could be 'ate' (e.g. I had an ice cream) and 'ate' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'to' is the link.
Can you help me to learn more?
(Other definitions for terminate that I've seen before include "Finalise" , "Close" , "Bring to an end" , "Stop" , "Cut short" .)