I initially looked up the meaning of this word and found out that it means literally the mouth of River Ness. However, in the play, this castle has been associated with evil and dark images and I was hoping if anyone could comment on some linguistic or semantic element of this very word that would have allowed Shakespeare to do so.
I think it is not the name itself but the facts that the name evokes: crimes, fires and the "dark" life of the Middle Ages":
Shakespeare’s tragedy ‘Macbeth’ was supposedly based in the earlier 11th century Inverness Castle, the location of Duncan’s murder. The present Inverness Castle may not be witness to anything so dramatic, but as the premises of the Sheriff’s Court it may not be without its own tales of crime and passion.
The 11th century Inverness Castle was made of wood and was destroyed by King Robert I. Today the only evidence is a part of the curtain wall and a restored well. It was later replaced by a stone fortress, built in 1548 on Castle Hill by George Gordon. He was the fourth Earl of Huntly and the Constable of the Castle at the time.
- literally "mouth of the (River) Ness (for which see Nessie), from Inver-, element in place names in Scotland of Gaelic origin, usually of places at the confluence of a river with another or the sea, from Old Irish *in(d)ber- "estuary," literally "a carrying in," from Celtic *endo-ber-o-, from *endo- "in" (from PIE *en-do-, extended form of root *en; see in) + from *ber- "to carry," from PIE root *bher- (1) "to carry" (see infer).
Echoing Josh61's response, I don't feel that there is tremendous significance to the place name other than to add to the play's overall "Scottishness."
We know that the play was written after 1605, thanks to allusions to the Gunpowder Plot. A number of scholars, including Alvin Kernan and A.R. Braunmiller, have suggested that the play was presented as a court entertainment during the state visit of King James's Danish in-laws in 1606. In any case, it is certain that Macbeth represents an attempt by Shakespeare's theatrical company - who had recently been renamed "The King's Men" - to curry royal favor and salute the new monarch and his Scottish origins.
It is unlikely that Shakespeare or many in his ordinary London audience had much direct knowledge of Scotland, so the collection of place and character names are most probably intended more to enrich the overall setting than to convey specifically encoded meaning.
And oftentimes, to win us to our harm, the instruments of persnickety scholarship tell us truths, win us with honest trifles to betray us in deepest consequence...