Almost noon: too soon (6)
I believe the answer is:
nearly
'almost' is the definition.
(synonyms)
'noon too soon' is the wordplay.
'noon' becomes 'n' (abbreviation).
'too soon' becomes 'early' (earlier than required).
'n'+'early'='NEARLY'
(Other definitions for nearly that I've seen before include "pretty much" , "Almost, well-nigh" , "Almost, not quite" , "More or less" , "parsimoniously" .)