In this post… The etymology of “tonic”. Is urea an effective osmole? The anatomy of the EFWC equation. How do NaCl supplements help in hyponatraemia? tonic, adj. and n. Medicine, etc. Having the property of increasing or restoring the tone or healthy condition and activity of the system or organs; strengthening, invigorating, bracing. (Of remedies or remedial treatment, and hence of air, climate, etc.) Etymology: Greek of or for stretching