1 : not present at a usual or expected place
They were talking about absent friends. [=friends who were not there]
an absent father who is not home most of the time
The soldier was absent without leave. [=AWOL; absent without having permission to be absent]
Most of the executives attended the meeting, but the company president was conspicuously absent. [=conspicuous by his absence; it was very noticeable that the company president was not there]
— often + from
She was absent from work/school on three occasions.
2 : not present at all : not existing
a gene that occurs in mammals but that is absent in birds
a landscape in which vegetation is almost entirely absent
— sometimes + from
Vegetation is almost entirely absent from the landscape.
3 always used before a noun : showing that a person is thinking about something else : showing a lack of attention to what is happening or being said
He made an absent reply to her question as he continued to watch the TV.
There was an absent [=distracted] look on her face.
— absently adverb
He replied absently to her question.