Shake the only hand of Tyr
Tyr (referred to as Tiw, Tiu or Tew in Old English) was the god of combat. He had just one hand and the story behind it is as follows.
The prophecy of the sybil that three siblings would bring troubles to gods alarmed the pantheon and Odin (see also the section for Wednesday) decided to get rid of them. One of them was Fenrir, a huge mythological wolf. They tried to bound him, but he was too strong and tore any chain they used.
Finally they asked dwarves to make a special, untearable binding called Gleipnir. It consisted of six wondrous ingredients which do not exist any longer because the gods took them from the world for good. These were the sound of a cat’s footfall, the beard of a woman, the breath of a fish, the roots of a mountain, the sinews of a bear (meaning rather sensibilities in this case) and the spittle of a bird.
Fenrir did not believe them that they would set him free again after having tried the binding on him. Tyr had to put his arm in his mouth as the guarantee. That is why one of his arms is missing. And again, when Ragnarok begins, the wolf will free himself from Gleipnir and avenge this deception by devouring Odin.
In Romance languages, this day belongs to Mars, the Roman god of war (martes in Spanish, mardi in French).