Legally united Irish body to speak pompously, at length (9)
I believe the answer is:
corporate
'legally united' is the definition.
'corporate' can be an answer for 'united' (I've seen this before). I'm not certain of the 'legally' bit.
'irish body to speak pompously at length' is the wordplay.
'irish body' becomes 'corp' (I am not sure about this - if you are sure you should believe this answer much more).
'to speak pompously at length' becomes 'orate' (I've seen this before).
'corp'+'orate'='CORPORATE'
Can you help me to learn more?
(Other definitions for corporate that I've seen before include "Joint" , "belonging to a large company" , "Of a legal entity acting as an individual" , "Relating to a large group or company" , "Poor crate could be legally united into a body" .)