The credit of this post goes to Mr. Rudrin Purakayastha. With his permission, I am simply editing as this post, his comments on my previous post, entitled “Concatenated Bengali names.” I have not checked the complete correctness of the views, but they seem logical…
Concatenation of surnames is not unique in Bengal, If you study in depth then you see that it is also present in other parts of our country like Thakore Desai, Dutt Chowdhury, Sinh Rathore, etc.
Bengali vaidyas started identifying themselves as off-shoots of Brahmin Father and Vaishya mother, calling themselves as either Sengupta or Sensharma (where Gupta indicates vaishya and Sharma brahmana). This practice is hardly 200-250 years old. There are vaidyas today with non-compounding surnames such as Das, Dutta, Kar, Sen, Gupta etc.
Most Bengali kayasthas have their surnames common with lower castes as Kayastha is not only an Kshatriya clan, but this also means writer in Sanskrit. This is a profession that can be taken by brahmins and other castes.That is why Purakayastha surname is also found in Bengali Brahmins.
Whenever an ancient bengali takes up the profession of kayastha he used to combine that title with his surname. Some examples:
SenMajumdar is a person with a surname Sen, but the profession of a Majumdar (similar to the Marathi word Mujumdar, which actually derives from the Pharsi majmuadaran).
GhoshMoulik: Kayastha Ghoshes are generally kulin but some of them are Moulik (not kulin) they use it to distinguish themselves.
Roy is a small jaminder and Roychowdhury is the bigger one.