“Tonic” in TCM specifically refers to herbs that:

1. increase Qi, usually through enhanced absorption and mitochondrial replication
2. nourish Blood, usually by regulating red and white blood cell replication (The term ‘tonify’ is not properly applied to either Blood or Yin in the body)- . Blood deficiency is always involved with nutritional deficiency.
3. nourish Yin, usually by counteracting dryness and by enhancing the hormones associated with the parasympathetic nervous system
4. tonify Yang, usually by warming and stimulating metabolism and nourishing or enhancing the hormone of the sympathetic nervous system

All four areas of “tonification” in TCM are involved with longevity. Ayurveda refers to all tonics as rasayanas. Rasāyana, रसायन is a Sanskrit word, with the literal meaning: Path (āyana) of essence (rasa). It is a term that in early Ayurvedic medicine means the science of lengthening lifespan, and in later (post 8th-century) works is sometimes referred to as Indian alchemy. Western definitions of “tonic” generally refer to:

1. nutritive tonic: herbs like comfrey, aloe gel, rhodiola, saw palmetto, alfalfa and others that significantly are used for their ‘nutritional’ value. Many people call nettle leaf a tonic, which it may be, but one would have to counterbalance any nutritional value it may have with its eliminative properties as a diuretic. Nettle seed and root, I think, could be properly called ‘tonics.’
2. bitter tonic: an herb that in itself may have little nutritional value but stimulates appetite and assists digestion, thus making food one eats more tonic.
3. any herb whose basic property as a demulcent, diuretic, diaphoretic, laxative or expectorant, among other properties for which it is primarily used, is facilitated and assisted

It is in this latter category where the anti-mucus, demulcent properties of mullein leaf might qualify. Mullein root is obviously more nutrient. The leaf in my opinion and this entire category of herbs whose properties have known ‘active therapeutic’ effects would be considered ‘tonic’ in the Western sense. I think given the deeper and long established sense of “tonic” in TCM or “rasayana” in Ayurveda, referring to herbs used for longevity and promoting hormonal processes, is the best definition and therefore use of the term ‘herb tonic.’