The Building of Barad-dûr

[Galin]

Barad would appear to imply a 'great towering building (fort, city, castle) tower', and also according to Tolkien, the root seems to express great height combined with strength, size, majesty. One of the Quenya words given for comparison is Tarminas. This is according to Tolkien's Words, Phrases and Passages, entry Elbereth.

However I couldn't find something post-Lord of the Rings for minas in this source (I thought there was something here!), so going back in external time to Etymologies (where we are dealing with N. meaning Noldorin not Sindarin, among other early differences)...

MINI -- stand alone, (...) Q. mindo isolated tower N. min 'one, single, distinct unique' minnas 'tower'

Again I wish I could remember a later reference, but with this (at least) I think we can see a semantic distinction.