Flirting having no head for marriage (8)
I believe the answer is:
alliance
'for marriage' is the definition.
(I've seen this before)
'flirting having no head' is the wordplay.
'flirting' becomes 'dalliance' (synonyms).
'having no head' means to remove the first letter (I've seen 'has no head' mean this).
'dalliance' with its initial letter taken away is 'ALLIANCE'.
(Other definitions for alliance that I've seen before include "Association for mutual benefit" , "Marriage - union" , "Federation" , "Bond" , "match?" .)