Ignorant individual blocks new reduced trail (8)
I believe the answer is:
nescient
'ignorant' is the definition.
(I know that ignorant can be written as nescient)
'individual blocks new reduced trail' is the wordplay.
'individual' becomes 'i' (Roman numeral for one).
'blocks' means one lot of letters goes inside another (the inside letters form a 'blockage').
'reduced' means to remove the last letter.
'trail' becomes 'scent' (an animal's trail is its scent).
'new' with its last letter taken off is 'ne'.
'ne'+'scent'='nescent'
'i' placed into 'nescent' is 'NESCIENT'.
(Other definitions for nescient that I've seen before include "Unaware of" , "Ignorant" .)