Busy disc jockey on ecstasy leaves part of speech (6)
I believe the answer is:
active
'busy' is the definition.
(similar in meaning)
'part of speech' is the wordplay.
'part' becomes 'act' (I have seen 'Part of play ' mean 'act' so perhaps 'part' could also mean 'act').
'of speech' becomes 'ive' (I can't explain this - if you can you should believe this answer much more).
'act'+'ive'='ACTIVE'
'disc jockey on ecstasy leaves' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for active that I've seen before include "On the go" , "Engaged, not idle" , "Moving about, functioning" , "Keeping busy or operative" , "Keeping busy, not lazy" .)