Fitzrover & drjax it is hard to explain 24 without spoilers but letters 5,6 and 7 make up a rather specific synonym for a word in the clue - specific in so much as I can only think of one context win which it is ever used with this meaning! I hope this helps rather than confuses you...
I don’t think there’s ambiguity in 7d. You wouldn’t say the answer with the ending occurring earlier in the alphabet if you meant the words that make up the definition. Or at least in my experience you wouldn’t. I’ve only ever heard it said using the other letter, the one occurring later in the alphabet.
Yevrah assuming that the Def of 25a is the final word of the clue there is an obvious answer that fits with the crossers but I don't understand the wordplay, perhaps I am barking up the wrong tree (or just barking)...