Having to eat indoors is a tough business (2,6)

'a tough business' is the definition.
The definition suggests an adjective which matches the answer.

'having to eat indoors' is the wordplay.
I cannot quite understand how this works, but
'eat' could be 'picnic' (picnicking is a kind of eating) and 'picnic' is located in the answer.
The remaining letters 'no' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'is' is the link.

Can you help me to learn more?