Last cult started off with one friend (8)
I believe the answer is:
ultimate
'last' is the definition.
(similar in meaning)
'cult started off with one friend' is the wordplay.
'started off' means to remove the first letter (I've seen 'starting off' mean this (the starting letter is removed)).
'with' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'friend' becomes 'mate' (mate is a kind of friend).
'cult' with its initial letter taken away is 'ult'.
'ult'+'i'+'mate'='ULTIMATE'
(Other definitions for ultimate that I've seen before include "Last or highest" , "Last possible, final" , "Last or final in a series or process" , "Happening at the end of a process, final" , "Last or concluding element" .)