Frustrating crossing a river? In no hurry (8)
I believe the answer is:
tarrying
'in no hurry' is the definition.
'frustrating crossing a river?' is the wordplay.
'frustrating' becomes 'trying'.
'crossing' means one lot of letters goes inside another.
'river?' becomes 'r'.
'a'+'r'='ar'
'trying' going around 'ar' is 'TARRYING'.
(Other definitions for tarrying that I've seen before include "waiting" , "using delaying tactics?" , "Loitering" , "Lingering, staying on" .)