1, 2. Element, component, constituent, ingredient refer to units that are parts of whole or complete substances, systems, compounds, or mixtures. Element denotes a fundamental, ultimate part: the basic elements of matter; resolve the problem into its elements. Component and constituent refer to a part that goes into the making of a complete system or compound. Component often refers to one of a number of parts: Lab work is an important component of the science course. Constituent suggests a necessary part of the whole: The constituents of a molecule of water are two atoms of hydrogen and one of oxygen. Ingredient is most frequently used in nonscientific contexts: the ingredients of a cake; the ingredients of a successful marriage.

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