middle name 
noun
1A person’s name placed after the first name and before the surname.We argued for several minutes coming up with possible first names but no middle names to go with them....
- She claimed she hated his first name and his middle name, Robert, was easily shortened to something she thought was much more preferable, so that's what she called him.
- Our children will have 2 middle names, my last name being the second, and his last name.
1.1A quality for which a person is notable: optimism is my middle name...
- As straight and honest as the day is long, with integrity his middle name, he has embellished politics for half a century and more.
- Discretion is my middle name, but let's just say it was a multi-tin deal.
- Discretion is not their middle name and they give such a fiery display as to be considered suitably decorative for pot plant use.