Рисова каша добре смакує з рибою ;)
Каша means a type of food made by boiling any kind of grains in water or milk. You can use an adjective before the word каша to make it clear what it's made of.
For example, рисова каша -- boiled rice, вівсяна каша -- porridge/oatmeal, гречана каша -- boiled buckwheat.
- Рис. You cannot refer to the dry grain being sold as 'каша'. Я придбав пакет рису -- I've bought a packet of rice.
- Both make good sense, but I believe that 'рис/вівсянка/гречка' are used more frequently than 'рисова каша/вівсяна каша/гречана каша' because these are shorter. Я з’їв тарілку рису (= рисової каші) -- I've eaten a plate of rice.
Interesting....I might have got this wrong due to a Lemko influence on me growing up, as we always called каша any type of processed or partially processed cereal/grain (whether it be cornflakes in milk, or cooked oatmeal or гречка - yum!). Given that my grandmother was a Lemko Ukrainian living on the Polish/Ukrainian border, this might be a general usage of the word "каша" by people from that area.