Not to be confused with pink fluffy unicorns dancing on rainbows, we have this:



I'm sorry to say, this is not a "unicorn rampant", because it is not a full-bodied unicorn, it is not facing to our left and it is not rampant.

This is a unicorn rampant:



What we are looking at on the arms of House Fortemps would be best described as:

Sable, a unicorn couped contourny in a wreath of thorns gules.

Sable = Black base colour
Unicorn = PONY!
Couped = creature is severed at the head with a clean cut
Contourny = preceding creature is facing to the right of the viewer
wreath of thorns = that, unless it's meant to be something else
Gules = designates everything preceding it back to the last mention of a colour, as red.

Blazon. It's a form of mangled French.