Declares King John 'boring, dense, interminable' (9)

'declares' is the definition.
The definition and answer can be both to do with social activities as well as being verbs in their -s form.
Maybe there's a link between them I don't understand?

'king john boring dense interminable' is the wordplay.
'king john' becomes 'throne' (I can't explain this - if you can you should give a lot more credence to this answer).
'boring' means one lot of letters goes inside another (some letters must 'bore' a hole into other letters).
'interminable' indicates the central letters (the ends or 'terminuses' of the word are removed).
The central letters of 'dense' are 'ens'.
'throne' placed into 'ens' is 'ENTHRONES'.

Can you help me to learn more?