Sojourn in centre of Boston okayed (4)
I believe the answer is:
stay
'sojourn' is the definition.
(I've seen this before)
'centre of boston okayed' is the wordplay.
'centre of' means to look at the middle letters.
'okayed' becomes 'ay' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The centre of 'boston' is 'st'.
'st'+'ay'='STAY'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for stay that I've seen before include "Wait" , "Abide" , "Visit (for the night)" , "Remain - support" , "Linger" .)