A force just before the start of secret liaisons (7)
I believe the answer is:
affairs
'liaisons' is the definition.
('affair' can be a synonym of 'liaison')
'a force just before the start of secret' is the wordplay.
'force' becomes 'F' (symbol used in Physics e.g. f=ma).
'just before' becomes 'fair' (I can't explain this - if you can you should believe this answer much more).
'the start of' says to take the initial letters.
The first letter of 'secret' is 's'.
'a'+'f'+'fair'+'s'='AFFAIRS'
Can you help me to learn more?
(Other definitions for affairs that I've seen before include "Business; amours" , "Business and financial dealings" , "Current ones are of interest to the public" .)