Holonymy (in Greek ὅλον holon, "whole" and ὄνομα onoma, "name") is a semantic relation. Holonymy defines the relationship between a term denoting the whole and a term denoting a part of, or a member of, the whole. That is,
'X' is a holonym of 'Y' if Ys are parts of Xs, or 'X' is a holonym of 'Y' if Ys are members of Xs.For example, 'tree' is a holonym of 'bark', of 'trunk' and of 'limb.'
Holonymy is the opposite of meronymy.
Holynymic/meronymic relations are considered from the paradigm of canonical/prototypical relations, i.e. that which is considered an essential component/characteristic/part of the unit in question. Cruse uses the example of a "door-handle" relation compared to a "body-ear" relation: not every "door" has a handle, essentially (e.g. sliding doors, swinging doors), but every "body" (i.e. human body) does have an "ear". He refers to the former as a "facultative" relationship. A handle represents an optional relation.