21st December is the Feast of St Thomas the Apostle, or Didymus. Thomas is known as Doubting Thomas as he was the apostle who wouldn't believe Christ had been resurrected until Christ appeared in front of him and he'd felt the nail wounds in Christ's hands and the wound in his side.
Thomas was known for his generosity, and the Tudors would commemorate his feast day by going "a-Thomasing", which was collecting alms.
There are also other traditions associated with the feast day, such as pie-making.
You can find out more about Thomas, the traditions associated with him, and his links to India in my talk...