PS. The 3 letter word at 17 D (or the 3 letter word reading upwards from 25 A) and 'Singular theme word' are all I have left. I'm trying to do something with those.
I think the highlighted words are the 4 letter we've been discussing plus it's synonym in the symmetrical 'opposite side' of the crossword. Still not sure what the third word is supposed to be.