The concept of the atom in ancient India derives from the classification of the material world in five basic elements by Indian philosophers.
This classification existed since Vedic times (c. 1500 BCE). The elements were the earth (prithvi), fire (agni), air (vayu), water (jaal) and ether or space (aksha). The elements were associated with human sensory perceptions: smell, touch, vision, taste and ether/space respectively.
Later, Buddhist philosophers replaced ether/space with life, joy and sorrow.
Ancient Indian philosophers believed that all elements except ether were physically palpable and hence comprised of minuscule particles. The smallest particle, which could not be subdivided, was called paramanu in Sanskrit (shortened to parmanu), from parama (ultimate or beyond) and anu (atom). Thus, "paramanu" literally means "beyond atom" and this was a concept at an abstract level which suggested the possibility of splitting atoms, which is now the source of atomic energy.
The 6th century BCE Indian philosopher Kanada was the first person who went deep systematically in such theorization.
Another Indian philosopher, Pakudha Katyayana, a contemporary of Buddha, also propounded the ideas of atomic constitution of the material world. All these were based on logic and philosophy and lacked any empirical basis for want of commensurate technology.