Lost all interest with the onset of rows between stars (12)
I believe the answer is:
interstellar
'between stars' is the definition.
(interstellar means between stars)
'lost all interest with the onset of rows' is the wordplay.
'lost' indicates an anagram.
'with' means one lot of letters goes inside another.
'the onset of' says to take the initial letters.
The first letter of 'rows' is 'r'.
'all'+'interest'='allinterest'
'allinterest' is an anagram of 'intestellar'.
'intestellar' enclosing 'r' is 'INTERSTELLAR'.
(Other definitions for interstellar that I've seen before include "realm of Star Trek" , "Occurring between stars" , "In deep space" .)