The phrase “Tom thumb” comes from the same fairy tale. Back in the times of King Arthur, lived a poor and infertile couple who longed for a son but remained as barren as they were poor. They invite a passing old beggar to take shelter in their humble home and he turns out to be Merilin traveling in disguise.

When he hears of their desire to have a son, even if was no bigger than a thumb, Merlin does a bit of magic that brings about the birth of the legendary but rather small, Tom Thumb. He’s a popular fellow and even the local fairy queen blesses him.

From here arose the idiom "Tom Thumb", which means a person of very small physical stature.