Skeleton

[soliloquy]

23 across Outstanding wedding day for a single engineer ?N?O?E UNDONE has been suggested but does it fit the clue? It looks like it is going to end in ONE (the "single" bit of the clue). Could the answer be an engineer?

[Mamyalynne]

D for Day replaces i for one in union (wedding) + E (Engineer)

[Mamyalynne]

i for 'a single' sorry

[soliloquy]

Where does "outstanding" come into it?

[Mamyalynne]

Undone - outstanding/unfinished

not done or finished.
"he had left his homework undone"

[fiction-factory]

If a task is outstanding it is not done/ undone

[Mamyalynne]

Undone

synonyms: unfinished, incomplete, half-done; not started, not done, unaccomplished, unperformed, unexecuted, unfulfilled, unconcluded, unattended to, omitted, neglected, passed over, disregarded, ignored, left, remaining, outstanding, deferred, pending, on ice, awaiting attention, (up) in the air; informalon the back burner
"some improvement work was to be left undone due to the cost"

[Davemano]

I have been doing this crossword for more years than I care to say, but this week is one of the most awkward ones ever.