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.
presence. 1  the state or fact of being present, as with others or in a place. 2  attendance or company: Your presence is requested. 3  immediate vicinity; proximity: in the presence of witnesses.