þéttari
þéttari is an Icelandic word. It is the comparative form of the adjective þéttur. þéttur generally translates to "dense," "thick," or "close." Therefore, þéttari signifies a greater degree of density, thickness, or closeness. The precise meaning in context depends on what is being described.
For example, if discussing liquids, þéttari would mean more viscous or less watery. When referring to physical