Frank beginning to snigger during ceremony? Not half (7)
I believe the answer is:
sincere
'frank' is the definition.
('sincere' can be similar in meaning to 'frank')
'beginning to snigger during ceremony? not half' is the wordplay.
'beginning to' indicates taking the first letters.
'during' becomes 'in' (I've seen this in other clues).
'not half' means to take half the letters.
The initial letter of 'snigger' is 's'.
'ceremony' cut in half is 'cere'.
's'+'in'+'cere'='SINCERE'
(Other definitions for sincere that I've seen before include "Free from deceit" , "(Of person) genuine" , "Showing genuine feelings" , "Honest, heartfelt" , "Free from pretence" .)