Atoms of the same element that have different masses are called isotopes. Different masses result when there are different numbers of neutrons. All atoms of a particular element have the same number...
Definition of absent. 1 : not present at a usual or expected place : missing was absent from class today sharing memories of absent friends She was conspicously absent [=her absence was very noticeable] at the meeting. absently. adverb He replied absently to her question. Examples of absent in a sentence.
(usually uncountable, plural absences) 1  A state of being away or withdrawn from a place or from companionship; the period of being away. [First attested around 1350 to 1470.] Absence makes the heart grow fonder. 2  Failure to be present where one is expected, wanted, or needed; nonattendence; deficiency.