Sentence:  But what was worse, <WSD>damp</WSD> now began to make its way into every house—<WSD>damp</WSD>, which is the most insidious of all enemies, for while the sun can be shut out by blinds, and the frost roasted by a hot fire, <WSD>damp</WSD> steals in while we sleep; <WSD>damp</WSD> is silent, imperceptible, ubiquitous. 
Meaning of the word marked with <WSD> tags:  Moisture; humidity; dampness.