Help to turn round ultimately tiresome day (8)
I believe the answer is:
befriend
'help' is the definition.
(a friend might help another friend)
'turn round ultimately tiresome day' is the wordplay.
'turn' becomes 'bend' (synonyms).
'round' indicates putting letters inside.
'ultimately' says to take the final letters.
'day' becomes 'fri' (abbreviation for Friday).
The last letter of 'tiresome' is 'e'.
'e'+'fri'='efri'
'bend' going around 'efri' is 'BEFRIEND'.
'to' acts as a link.
(Other definitions for befriend that I've seen before include "Become mates with" , "Become pals with (someone)" , "Finer bed (anag.)" , "Become a pal to" , "Become a companion to" .)