Full Idea
Is it true that we cannot say, non-circularly, what red is? We cannot find a complex synonym for it, but I think we can provide red with an ostensive real definition.
Gist of Idea
Simple things like 'red' can be given real ostensive definitions
Source
E.J. Lowe (What is the Source of Knowledge of Modal Truths? [2013], 6)
Book Reference
-: 'Mind' [-], p.24
A Reaction
I'm not quite sure how 'real' this definition would be, if it depends on observers (some of whom may be colourblind). In what sense is this act of ostensions a 'definition'? You must distinguish the colour from the texture or shape.