cred ‧ u ‧ lous /ˈkredjələs, ˈkredjʊləs $ -dʒə-/ BrE AmE adjective formal
[ Date: 1500-1600 ; Language: Latin ; Origin: credulus , from credere ; ⇨ ↑ credence ]
always believing what you are told, and therefore easily deceived SYN gullible :
Quinn charmed credulous investors out of millions of dollars.