Major, for one, to marry at sea, skirting duty (4,7)

'major for one' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'marry at sea skirting duty' is the wordplay.
'at sea' indicates anagramming the letters.
'skirting' indicates putting letters inside.
'duty' becomes 'office' (office is a kind of duty).
'marry' anagrammed gives 'armyr'.
'armyr' going around 'office' is 'ARMY OFFICER'.

'to' is the link.

Can you help me to learn more?