Witches put a strain on city (8)
I believe the answer is:
coventry
'city' is the definition.
(Coventry is an example)
'witches put a strain' is the wordplay.
'witches' becomes 'coven' (I've seen this in other clues).
'put' means one lot of letters go next to another.
'a strain' becomes 'try' (I've seen this in another clue).
'coven'+'try'='COVENTRY'
'on' is the link.
(Other definitions for coventry that I've seen before include "City (for those banished from society?)" , "English city" , "Where Lady Godiva rode" , "Has a 5 across designed by Basil Spence" , "West Midlands city" .)