Unknown (13)
'unknown' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for anon that I've seen before include "Without known author" , "Of unknown name (abbr)" , "devoid of credit" , "Not identified by name" , "In due course" .)
(Other definitions for indeterminate that I've seen before include "uncertain result?" , "Inconclusive" , "Vague - unsettled" , "Not exactly defined" , "Not precisely fixed" .)