Believe it or not, these two similar words have very different origins. An “outcast” is someone who has been cast (thrown) out of a group, and may be used loosely of all kinds of loners.
An “outcaste” is technically a South Asian person who has been expelled from his or her caste, or a person who lacks a caste identification. Although this spelling can be used metaphorically, it is probably better to confine it to discussions of social relations in Hinduism and other South Asian contexts.
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