Possibly related: "Seme, the smallest unit of meaning recognized in semantics". [1]
I was distracted, trying to think of where I'd seen something like that in science fiction, and now I think (but can't check right now) that Robert Heinlein's novelette "Gulf" had something about the smallest unit of thought; the "psychon" or some such.
There may also have been something in Keith Laumer's "The Great Time Machine Hoax", but I'm less sure about that.
The true minimum meaningful computation is probably the lambda function, anyway.
But since such things usually suffer from the Turing Tarpit [4], perhaps there's one that has some kind of minimax to be ideally terse and require ideally-few steps for its Turing equivalency, similar to the way that radix 3 (closest to e) has been claimed to have been proven to be the ideally efficient representation system. [5]
(I say "claimed" simply because I recently saw a claim that there's a loophole in the usual reasoning.)
[1] http://en.wikipedia.org/wiki/%C5%81ukasiewicz_logic#Real-val...
[2] https://en.wikipedia.org/wiki/One-instruction_set_computer
[3] https://en.wikipedia.org/wiki/Semi-Thue_system