A vulgar
slang used by Assamese
people (a language in
India) to say that someone has big and firm breasts.
Rik in Assamese means something which big and powerful and
shit comes from the Sanskrit word stanashit which means firm breasts.
Some people consider the word offensive and use a English replacement such as booby or titsy instead.
The new generation have started using rikshit on obese males too, probably because their body fats create the impression of breasts. But it seems that these people don't really mind being called rikshit and usually respond with a grin.