Arūpa (Template:Lang-Deva) means formless. It is the antonym for rūpa, and is used to refer to non-physical (i.e., non-material) subjects. It appears in Hinduism, such as in the description of Nirguna Brahman. It is also used in Buddhism.
Ether (akasha in Sanskrit) is somewhat arūpa, while classical elements are more rupa.[1]