Credulous

Lyusya is a very naïve and credulous girl.

Did you know "credulous" is not in the dictionary?

He's so credulous. He takes everything you say at face value.

It is extraordinary how credulous the peasants are about here!

He's smart; he's just credulous.

"Tom's not very smart, is he?" "No, he's smart; he's just... credulous."

[…]purſued his vnneighbourly purpoſe in ſuch ſort: that hee being the ſtronger perſwader, and ſhe (belike) too credulous in beleeuing or elſe ouer-feeble in reſiſting, from priuate imparlance, they fell to action; and continued their cloſe fight a long while together, vnſeene and vvithout ſuſpition, no doubt to their equall ioy and contentment.

The doctor was a small, black, plump man with fuzzy hair and round, credulous eyes.

'Twas he possess'd me with your credulous death

The powerful mind of Aristotle, which led him to reject with disdain the credulous tales and fabulous stories of the age, can nowhere be traced in the writings of Pliny, whose works, on the contrary, abound in fables and in prodigies, at once manifesting that weakness of mind inseparable from credulity, or that disinclination to investigate truth, which is the sure mark of a secondary order of intellect.