Thurisaz means jötunn or giant (Thurs), the Anglo-Saxon version is Thorn – which hasn’t changed in meaning and still means thorn like you find on a plant. Some writers suggest thorn was a kenning for giant but I have not been able to confirm this and can’t see any obvious reason why it would fit.
The Anglo-Saxon rune poem says “The thorn is exceedingly sharp, an evil thing for any knight to touch, uncommonly severe on all who sit among them.”
Jötnar or Thurs appear throughout the Norse Myths, usually as opponents of the Aesir, although there are plenty of friendlier encounters too. In fact sometimes it can be difficult to tell where the gods end and the giants begin. Several gods married giants, including Frey, and Njord Loki was half giant half god, and if you go back to the beginning both gods and giants have the same ancestral roots. The Aesir and the Jötnar were descended from the giant Ymir, all of the nine worlds were formed from the giants remains after he was killed so it could be said that all life originates with the giants. I tend to think of the Jötnar as the primal forces of nature and chaos. The constant obstacles to order and progress. We wouldn’t be anything without them, but part of being human is our attempts to control and shape them.
I find it easier to think of thorns rather than giants, the glyph even looks like a thorn on the stem of a plant. There is something equally wild and challenging about thorns. So many of the tastiest berries you can pick are protected by vicious thorns. Blackberries and gooseberries are common examples but sloes, lemon trees, wild apples, chestnuts, and quince all have thorns too. Even though we seldom eat the hips these days roses have thorns. Thorns were an evolutionary tactic to protect fruit from grazing animals, they are an obstacle and a deterrant. Nature putting up a fight. You see this in stories too. The wall of thorns that grew around Sleeping Beauty’s castle was enough to keep intruders out for 100 years.
Thurisaz then is a challenge a barrier or an obstacle. It’s not usually agressive, it won’t pay you any notice if you keep away but if you interact with it you need to do so carefully or you can expect it to hurt.