4 D isn't Fill - it's an odder, less usual word.
6 D. Is a two-letter word for 'space' (a printing term, used a ,lot in crosswords) and an everyday word for Stable (as in steady).
18 A was an odd word, it was an 'o' that was removed.
PS I always think it's better to give the clues, but I don't have time to add them!