Definition from Wiktionary, the free dictionary
Eponym for the Apostle Thomas.
- Now Thomas, one of the twelve, called the Twin, was not with them when Jesus came. So the other disciples told him, "We have seen the Lord." But he said to them, "Unless I see in his hands the print of the nails, and place my finger in the mark of the nails, and place my hand in his side, I will not believe." Eight days later, his disciples were again in the house, and Thomas was with them. The doors were shut, but Jesus came and stood among them, and said, "Peace be with you." Then he said to Thomas, "Put your finger here, and see my hands; and put out your hand, and place it in my side; do not be faithless, but believing." Thomas answered him, "My Lord and my God!" Jesus said to him, "Have you believed because you have seen me? Blessed are those who have not seen and yet believe." Now Jesus did many other signs in the presence of the disciples, which are not written in this book; but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in his name. — John 30:24-31 KJV
doubting Thomas (plural doubting Thomases)
one who requires proof