The voice used in the British version of Siri, which is identical to the "Daniel" voice on Mac OS 10.7 (Lion) and above, reads out the word "profoundness" as "profundity".
This substitution happens on iOS Siri in British mode, and in all versions of Daniel on Mac OS 10.7 through macOS 10.12 Sierra, except it does not happen on the "Compact" version of Daniel that is present before the high-quality version is downloaded on 10.12.
Since the string "profound" does not occur in any of the files under /System/Library/Speech/Voices/Daniel.SpeechVoice on a Mac, it is not possible to see what other word substitutions happen just by reading strings out of the binary file. So I would like to ask if anyone knows what other substitutions are made.
It is slightly worrying to blind people who rely on voice synthesis to read the screen, because it means the voice cannot be relied on to read all the words exactly as they are, which might be very important in a legal setting. (I cannot think of a real example with the particular case of "profoundness" versus "profundity", other than reading a poem because "profoundness" rhymes with "soundness" but "profundity" does not, but if other words are changed then they might be more serious.)
I do also wonder why this substitution was added (if anyone knows). My wild guess is that some early development version of the voice had a glitch that was exposed by making it try to say "profoundness", so a developer added the substitution as a workaround, but it was left in the system even when no longer needed (except it was removed from the "Compact" version of the voice). I suppose it's also possible that some developer was under the mistaken impression that British people always read "profoundness" as "profundity".
We should probably report this as a bug, but I'm asking it as a question here first in case anyone knows any other words that are changed by this voice, so that we can make a more comprehensive bug report to Apple (and Nuance/Scansoft who licensed the voice to Apple).