Requirement to be born on the first of December (4)
I believe the answer is:
need
'requirement' is the definition.
('need' can be a synonym of 'requirement')
'born on the first of december' is the wordplay.
'born' becomes 'nee' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'the first of' indicates taking the first letters.
The initial letter of 'december' is 'd'.
'nee'+'d'='NEED'
'to be' acts as a link.
(Other definitions for need that I've seen before include "Necessity" , "Call" , "Rely on" , "''A friend in .... is a friend indeed''" , "Require (as essential)" .)