"whodunit"(who done it?) tarzındaki "misteri" hikayelerinden aparılarak türetilmiş bir kelime.
ingiliş bir açıklaması urban dictionary'de yapılmış, aynen kopi peyst ediyorum:
--spoiler--
1. Using a personal deity as defined by a self described holy text such as the Holy Bible or Torah, for example, to describe the natural functions and phenomena of any part(s) of the universe.
2. Often associated with a lack of education or a fundamental lack of understanding of science. Although it is more likely due to the person's unwillingness to accept scientific theory even if they do understand because it disagrees with their religious beliefs. Some religious people have gone to great lengths to prove their goddunit ideas with pseudo-sciences like creationism. Creation museums have even been opened in the United States although it is against federal law for creation to be taught in school as it has no scientific basis.
3. Used in a derogatory way to insult a person's willingness to push away all other things which disagree with his religious interpretation of the perplexities of nature. Derived from the words "God done it" to popularized by people who live in the southern states of America where it is more acceptable to use improper grammar.