Menon is a sub-caste of Nambiar community now. A member of Nambiar Mahasabha told me that all General Category Menons are now the members of Nambiar Mahasabha. Nambiar Mahasabha was formed in the year 2017. Male ancestors of General Category Menons used to work under the Hindu kings. Among the Non-Royal communities of Malabar and Kochi regions, only women of Menon and Nambiar families were and are permitted to marry the men of Hindu Royal families.
I don't know the meaning of the word Menon. In Marathi, Mena means palanquin. Thanjavur of Tamil Nadu and some parts of Northern Malabar in Kerala were once under the rule of Maratha Kings. In Tamil, Menapallakku means Palanquin. So, Menon doesn't seem to be a Malayali word. Nair and Bunt are two entirely different communties. But there is a similar surname called Menava in the Bunt community.
In the Nair community, there were three types of Menons. They were Paricha Menon, Menon Panikkar, and Pattola Menon, the relative rank of each often varying from Taluk to Taluk.
Once I read in a website that Paricha Menons are highest among the Menons. Pattola Menons were the secretaries of the Nilambur Thirumulpads. The first Pattola Menon was one Shri. Kelu Menon who was reputed for his knowledge of toxicology and cures for snake-bites. Thazhakodenadu of Themmalapuram Taluk which was under Sekhari Varma Raja of Palghat was governed by the first Naduvazhi, Kanhumalpada Nair and the second governor Tharupada Nair and the Raja's accountant (Pattola Menon) was Anavangot Menon and the governors were Nannat Menon and Kulaviyil Menon respectively.
Shri.Kelu Menon of Perumpulaavil Menon Tharavadu was an expert in Kalarippayattu. He was best known for his swordsmanship and was able to reach the heights by backflipping. Because of his martial prowess, Shri.Kelu Menon at the time was appointed as the village headman. Even then he did not entirely give up his wild days and was once very nearly caught while raiding a rich merchant's house in Kunnamkulam near Thrissur, supposedly in Robin Hood style of robbing the rich to help the poor. Gradually his reputation spread, and he became quite a folk hero.
Data were collected from The Indian Forester - Volume 51 - Page 118. Pattola Menon. — Recorded, in the Cochin Census Report, 1 90 1, as a sub-caste of Nayars, who are accountants in aristocratic families, Castes and Tribes of Southern India - Volume 1 By Edgar Thurston and Kandur Rangachari, Tales Once Told: Legends of Kerala
By Abraham Eraly, Kavalappara papers by K. K. N. Kurup, University of Calicut, Dept. of History, Calicut University, 1984 - Kerala (India), Aitheehyamaala by Shri.Kottarathil Shankunni Warrier and Wikipedia.