John 20:27

Be not [μ η γ ι ν ο υ]. Literally, become not. Thomas was in a fair way to become unbelieving, through his doubt of the resurrection.

Faithless - believing [α π ι σ τ ο ς - π ι σ τ ο ς]. There is a correspondence of the words here, to which, perhaps, the nearest approach in English is unbelieving, believing.