I killed a plant ...

[brownelephant]

... a little tangerine (from seed) tree.

any chance it's not really dead and just resting?

it lives out on the patio in summer, living room (light and not too hot) in winter.

was in full leaf around christmas, last leaf dropped a week ago.

Well... it doesn't look too hopeful! Don't give up though, it might be taking a rest and has dropped its leaves for winter. Perhaps you could keep it slightly damp, and see what happens in a few weeks.

I hope so.
I keep watering it and hope for the best.
wondering if with some pruning I could revive it?

Do you have any tomatorite? If so I would be giving a regular fed of it instead of just water to try to encourage green growth.

would ordinary plant food do?

Yes any would feed the plant. Tomatoerite is particularly good for green growth but a general purpose food will fed it. Anything in a pot will need regularly feeding as it will use up the nutrients in the potting soil.

I thought your thread title was a new Katy Perry song!

Me too fuzzy

Now it's stuck in my head!

OP it looks a little on the crispy side. Worth getting another couple on the go from seed? By the time they germinate the weather should be improving