Viscosity comes from Medieval Latin 'viscositas', from Late Latin 'viscosus' ('sticky'), from Latin 'viscum' ('birdlime, mistletoe'), a sticky substance. In current use it is a noun meaning "a fluid's resistance to flow; thickness or stickiness". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The history is mainly one of transmission into English, with the older form and sense carried through borrowing or adaptation. The historical chain includes Latin viscositas and Latin viscum. Related English forms include viscous, viscid, and viscose. For dictionary purposes, the important point is the continuity between the older form, the route into English, and the present lexical sense.