"instrument for determining the relative density of solid bodies," by 1858; see pycno- + -meter.
Entries linking to pycnometer
pycno-
before vowels pycn-, word-forming element meaning "close, thick, dense," from Latinized combining form of Greek pyknos "thick, dense, solid, compact; numerous; strong; brave; clever," which is of uncertain origin. Often in English via German as pykno-.
-meter
word-forming element meaning "device or instrument for measuring;" commonly -ometer, occasionally -imeter; from French -mètre, from Greek metron "a measure," from PIE root *me- (2) "to measure."