Related Clues:

• Amalgamates
• Becomes one with
• Altars one's status?
• Rings up?
• Forms a family
• Makes two into one
• One might choose to come before this, by the sound of it, when one get married
• When one has a 21 across by day
• The day's got shorter when one gets married
• Becomes a missus
• One day makes one
• Joins in matrimony
• Creates a union
• Joins as a couple
• Puts one and one together?