Presiding officer joins second summit with hesitation (7)
I believe the answer is:
speaker
'presiding officer' is the definition.
(speaker is a kind of presiding officer)
'second summit with hesitation' is the wordplay.
'second' becomes 's' (common abbreviation).
'summit' becomes 'peak' (mountain peak).
'with' is a charade indicator (letters next to each other).
'hesitation' becomes 'er' (sound made while hesitating - um, er).
's'+'peak'+'er'='SPEAKER'
'joins' acts as a link.
(Other definitions for speaker that I've seen before include "Presiding officer of the US House of Represtatives" , "He asks for order" , "Leader of the majority party in US House of Representatives" , "Commons presiding officer" , "Parliamentary authority" .)