Hi Ciaran
I just found it! 
 
It's in nexus.min.css:
.hornav > ul > li > ul > li > a::after, .hornav > ul > li ul > li > ul > li > a::after {
	content: attr(title);
}
So, in custom.css I added:
.hornav > ul > li > ul > li > a::after, .hornav > ul > li ul > li > ul > li > a::after {
	display: none;
}
For better understanding, here some screenshots:
Setting in menu link:
	
 
How it looks like in frontend:
	
 
HTML code:
	
 
Patrick