someone who has difficulty believing something; a skeptic
—You’ll have to convince all the doubting Thomases on the board before you’ll get any funding for your plan.

After Jesus died, on a Friday, his body was placed in a tomb. Then, on the following Sunday, some of Jesus followers went to the tomb and found that the large stone covering the opening had been rolled away, and Jesus’ body was gone. Later that day, Jesus, alive, came to the disciples, to show them that he had been resurrected. But one disciple was missing from the group: Thomas. When he heard what had happened, he said,

“Unless I see the wounds from the nails in his hands, and put my finger into the wounds from the nails, and put my hand into his side, I will never believe it!”

Eight days later the disciples were again together in the house, and Thomas was with them. Although the doors were locked, Jesus came and stood among them and said, “Peace be with you!” Then he said to Thomas, “Put your finger here, and examine my hands. Extend your hand and put it into my side. Do not continue in your unbelief, but believe.” Thomas replied to him, “My Lord and my God!” Jesus said to him, “Have you believed because you have seen me? Blessed are the people who have not seen and yet have believed.” (John 20:25-29)