Humdrum existence of Rugby Union team originally (3)
I believe the answer is:
rut
'humdrum existence' is the definition.
(as in the phrase 'she's in a rut at the moment')
'rugby union team originally' is the wordplay.
'rugby union' becomes 'ru'.
'originally' says to take the initial letters.
The first letter of 'team' is 't'.
'ru'+'t'='RUT'
'of' is the link.
(Other definitions for rut that I've seen before include "Deep tyre track" , "Furrow made by wheels" , "Deep groove as in a lane" , "Furrow or groove as in track" , "Groove made by wheel" .)