Short cone and tall cone share an end (8)
I believe the answer is:
conspire
'end' is the definition.
Although both the answer and definition are verbs in their base form, I can't see how one could define the other.
'short cone and tall cone share' is the wordplay.
'short' means to remove the last letter.
'and' is a charade indicator (letters next to each other).
'tall cone share' becomes 'spire' (I can't explain this - if you can you should believe this answer much more).
'cone' with its final letter taken off is 'con'.
'con'+'spire'='CONSPIRE'
'an' is the link.
Can you help me to learn more?
(Other definitions for conspire that I've seen before include "'Plot, connive (8)'" , "Plot together - on prices (anag)" , "So prince is given to plan secretly with others" , "Secretly plan together" , "Collude" .)