Wikipedia
Nambidi is a caste of Kerala, India. They are considered to be half- Brahmin and half- Kshatriya, and to have originated when a section of the Nambudiris was degraded or a section of the Nairs was upgraded in the caste system.
Nambidis are divided into two: the ones who wear the sacred thread and perform the Upanayanam and the ones who do not. The former are Nambudiris who were degraded to the Brahmakshatriya status since their ancestors had committed a heinous act by murdering a ruler of Kerala. On their return the other Nambudiris welcomed them but they refused to seat themselves with the other Brahmins owing to the sin they committed and instead sat on the steps of the hall. They came to be known as Nom Padimels or those on the steps and this term was later corrupted into Nambidi. The latter are Nairs who were assigned the Nambidi title.