Married vets regularly employed by Post Office (8)
I believe the answer is:
espoused
'married' is the definition.
('espouse' can be a synonym of 'marry')
'vets regularly employed by post office' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'employed' becomes 'used' ('use' can be a synonym of 'employ'**).
'by' says to put letters next to each other.
'post office' becomes 'po'.
The alternating letters of 'vets' are 'es'.
'used' put after 'po' is 'poused'.
'es'+'poused'='ESPOUSED'
(Other definitions for espoused that I've seen before include "Adopted, as of a cause" , "embraced" , "Championed or took up cause" , "Gave one's support to" , "Advocated" .)