Become viscous or dense (7)
I believe the answer is:
thicken
(Other definitions for thicken that I've seen before include "(Of a plot) become more complicated" , "Become more dense (as plots do)" , "Clot" , "get fatter?" , "Make less flowing" .)
I believe the answer is:
thicken
(Other definitions for thicken that I've seen before include "(Of a plot) become more complicated" , "Become more dense (as plots do)" , "Clot" , "get fatter?" , "Make less flowing" .)