Gullible person led by visionary’s material (10)
I believe the answer is:
seersucker
'material' is the definition.
(I know that seersucker is a type of material)
'gullible person led by visionary's' is the wordplay.
'gullible person' becomes 'sucker' (sucker can mean a foolish or gullible person).
'led by' means one lot of letters go next to another.
'visionary' becomes 'seer' (synonyms).
'sucker' after 'seer' is 'SEERSUCKER'.
(Other definitions for seersucker that I've seen before include "Material" , "Cotton" , "Puckered fabric" .)