One can't be both at once? Boring! (4-3-5)

'one' is the definition.
Both the definition and answer are adjectives.
Perhaps there's an association between them I don't understand?

'can't be both at once? boring' is the wordplay.
I cannot quite see how this works, but
'be' could be 'live' (to be is to live or exist) and 'live' is present in the answer.
'boring' could be 'dead' (I've seen this in other clues) and 'dead' is found in the answer.
The remaining letters 'anda' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?