atomic clock (not to be confused with radio clock)

time / hour / the hours or time when something happens

measurement

measure

to use / to employ / to make use of, to apply / to spend

accurate; exact; correct; precise

accuracy; exactness; correctness; precision

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend

distal demonstrative, something far off removed from both speaker and listener: that, yon / particularly, male personal third person pronoun: he / by extension from he: boyfriend

he; boyfriend