chronometer (n.)

before vowels chron-, word-forming element meaning "time," from Latinized form of Greek khronos "time, a defined time, a lifetime, a season, a while," which is of uncertain origin.

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."