Sorry! I assumed it was too obvious to mention.
That is if you are using a facet based navigation with a topic map, it will return/navigate the facet you ask for, and also return/navigate any semantically equivalent facet.
One of the advantages of using a topic map to underlie a facet system is that users get the benefit of something familiar, a set of facet axes they recognize, while at the same time getting the benefit of navigating semantically equivalent facets without knowing about it.
I suppose I should say that declared semantically equivalent facets are included in navigation.
Declared semantic equivalence doesn’t just happen, nor is it free.
Keeping that in mind will help you ask questions when sales or project proposals gloss over the hard questions of what return you will derive from an investment in semantic technologies? And when?