23d is a homophone for the 2nd, 3rd, 4th and 5th words, and the definition is a particular meaning of the final word. In 10a the second word is the (final word of clue) where the first word goes.
Chrise, re your post @32, I was in IT for most of my working life before I retired (including 15 years in an I.T. consultancy firm) and I have never heard of that meaning of 5d!