Final answer:
The term that best defines thick mucus secreted by the respiratory lining is Viscous.
Step-by-step explanation:
The term that best defines thick mucus secreted by the respiratory lining is Viscous. In normal lung tissue, respiratory epithelial cells secrete mucus to trap dust, bacteria, and other debris. Cilia on the epithelial cells then move the mucus and its trapped particles up the airways. The mucus needs to have a thin, watery consistency to be effectively moved upward.