Seldom encountered (4)
I believe the answer is:
rare
'seldom encountered' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rare that I've seen before include "Singular, infrequent" , "Very lightly cooked, meat say" , "Unusual(ly fine)" , "Very scarce, hardly cooked" , "Very scarce like valuable antique" .)