Imposed on someone as anobligation, especially due to one'soffice.Proper behavior is incumbent on all holders of positions of trust.SpratAll men, truly zealous, will perform those good works that are incumbent on all Christians.Lying; resting; reclining; recumbent.(botany) Resting on something else; in botany, said of anthers when lying on the inner side of the filament, or of cotyledons when the radicle lies against the back of one of them.(zoology) Bent downwards so that the ends touch, or rest on, something else.the incumbent toe of a birdBeing the current holder of an office or a title.If the incumbent senator dies, he is replaced by a person appointed by the governor.
Simple Definition of incumbent

: a person who holds a particular office or position

    Full Definition of incumbent1:  the holder of an office or ecclesiastical benefice2:  one that occupies a particular position or placeExample 
When Reagan and Clinton were seeking re-election, they didn't go after their opponents directly, in part because they didn't have to. Those incumbents knew that there's a point at which strong and tough can look weak and desperate.