Number wait, losing heart, for legal official (6)
I believe the answer is:
notary
'legal official' is the definition.
(I've seen this before)
'number wait losing heart' is the wordplay.
'number' becomes 'no' (abbreviation).
'wait' becomes 'tarry' (to tarry is to wait or linger).
'losing heart' says to hollow out the word (remove centre letters).
'tarry' with its centre removed is 'tary'.
'no'+'tary'='NOTARY'
'for' acts as a link.
(Other definitions for notary that I've seen before include "One authorised to certify legal documents" , "Public official, usually a solicitor" , "One drawing up legal documents" , "Person who may certify legal documents" , "Person legally authorised to witness signatures" .)