Mhh, not sure about that. It depends a bit how much heavy lifting the
"or similar superhuman power" can do. If this is not a deity (and the
definition of "God" doesn't rule that out, as it is limited to persons,
not powers, and anyway only states necessary conditions) then there are
possible religions that are at the very least non-theistic, and that
means their adherents fit the second prong of the above definition of
atheist.
Candidate religions could be e.g. forms of ancestor worship. And it
could even go further. I don't consider the term "secular religion" a
contradiction in terms myself, and would argue that from the 18th
century onward, and Rousseau coined the term "civic religion" for this:
a personified vision of the nation state became the secular religion of
choice, appropriating all the trappings of religions. Personification
(Marianne, Uncle Sam), rituals (saluting the flag), symbols (flags,
again), communal singing (national anthems) other communal celebration,
often with fireworks to cast out demons (4th July, last night of the
proms), holy texts (constitutions) and of course a license to kill
unbelievers both foreign and domestic en mass, As a power that
transcends the individual, I'd say with a bit of good will "nations" can
be subsumed under "superhuman power that demands obedience"
Leaving that aside, while the OED definition tracks how most people use
the term in ordinary language, it is a bad fit for the way the terms
would be used in theology, sociology and anthropology of religion, so
deviating from it would not be a big deal. Some form of Buddhism e.g are
non-theistic/atheist, and still would be included even in a discussion
within comparative theology which tends to use narrower definitions of
religion than say sociologists (though what makes the picture a bit more
complicated is that historically most Buddhists would also follow a
local religion and import a deity from there, e.g. a city deity)
Even closer to home, there were historical examples of movements that
were both religious and explicitly atheist - Robespierre 's "religion
of pure reason: during the French revolution e.g, including the
"veneration" of the leaders of the revolution. Another influential
variety was Hebert, and his celebration of the goddess "Reason" in Notre
Dame Cathedral on 10 November. "Goddess" here in a strictly secular
sense: Antoine Momoro, his friend, wrote thus:
"Liberty, reason, truth are only abstract entities.
In the true meaning, they are not gods,rather,
they are part of ourselves."
From that it was one short step to deify the collective, or as Baron de
Cloots (the self styled "personal enemy of god) put it, "there is only
one God, Le Peuple" In the temples, you'd therefore get everything from
anthropomorphic representations of 'reason" to that of
"the people", and the worship intentionally carried out in church
buildings taken over by the revolution.
The "Religion de l'Humanité or église positiviste" would be another
example of a secular religion, created by Auguste Comte with chapels of
Humanity in France and Brazil still in use.
In the early 20th century, there was a lively debate within European
humanist organizations whether it would be a good idea to turn the
movement into a religion, and in modern times Alain de Botton, in his
"Religion for atheists" same the same point
I'd argue that all these discussions were about substantive points, the
participants were not confused about mere word meaning, so the OED
definition is just incomplete.