of a door slightly open

slightly open

not closed; allowing (things, people) to go in, out, through; not enclosed, fenced in, barred or blocked

unfastened, unclosed

(of hair) loose, not tied; (of a book) without a cover

undo

to take the cork from (a bottle)

clear, expose; spread

of undo

open

to untie, unfasten, loosen (knots, buttons etc); to destroy (something good) and bring back the (bad) state of affairs that existed before

open

to use a key to open a lock on (a door, cupboard etc)

open; solve