Limit small space below second property (8)
I believe the answer is:
straiten
'limit' is the definition.
(I've seen this before)
'small space below second property' is the wordplay.
'small space' becomes 'en' (in printing, a space as wide as a letter 'n').
'below' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'second' becomes 's' (common abbreviation).
'property' becomes 'trait' (both can mean a quality or feature).
's'+'trait'='strait'
'en' after 'strait' is 'STRAITEN'.
(Other definitions for straiten that I've seen before include "distress" , "Train set (anag.)" , "Restrict" , "Limit" .)