A வடசொல் type: a Sanskrit word borrowed into Tamil with its sounds adapted, because the original used letters or sounds Tamil doesn't have.

ரிஷபம் has no clean Tamil equivalent for its sounds, so it settled into இடபம்; பங்கஜம் became பங்கயம், வருஷம் became வருடம் - each one softened just enough to fit Tamil's own letters.

பங்கஜம் -> பங்கயம், ரிஷபம் -> இடபம், வருஷம் -> வருடம்.