con-: together, with
sist: derived from Latin "sistere", meaning "stand"
-o-: a linking vowel inserted interconsonantally between two morphemes
-meter: the instrument of measuring something
So consistometer means:
The instrument of measuring the degree of standing together.
If the physical substances stand together tightly, it must be thick, smooth or viscous. So consistometer means "an instrument for measuring the degree of being viscous".
Evolution of usage
The instrument of measuring the degree of standing together is not common in daily life
The consistometer is not common in daily life.