The OED’s definition of Derrida’s notion of différance is, ‘The impossibility or indefinite deferral of any ultimate or metaphysical signification, on account of the constantly changing and proliferating relationships between the linguistic signs in any sentence or utterance’. Dictionary definitions are in fact antithetical to the idea of différance: a standard, textbook way of explaining the theory is to point out that a dictionary can never make meaning de-finite, because each definition comprises yet more words to look up. (It’s the opposite of Wikipedia’s ‘Getting to Philosophy’ – or is it the same?) So the OED definition of différance takes one to those of impossibility, metaphysical, relationship, etc.
An exception to this is the OED’s definition of Butskellism, which I rewrote last week for my own of Osballs. Butskellism, the definition reads, is ‘The economic policy of Butler, regarded as largely undifferentiable from that of his predecessor and Shadow Chancellor Gaitskell’. But I look up undifferentiable and there are ‘No dictionary entries found’. This is the only example I’ve seen of a non-technical term being employed in an OED definition despite being itself undefined.*
* Sunday, 3rd July 2016: other examples are scuffling-plough, used in the definition of wing-bar, and self-aggrandizing, used in that of smack talk.