illustrate Copy link • illustrate: illustro, 1 (to shed light upon a subject): to explain and i. an obscure and unknown point of law, jus obscurum atque ignotum patefacere et il., Cic. See also to explain. Phr.: to i. a subject by instances, exempla alicujus rei proferre, adducere, supponere: cf. Cic. Inv. 2, 51, fin.