noun

• (countable) An addition or annex to a group, set, or total.
• (uncountable) The act of including, i.e. adding or annexing, (something) to a group, set, or total.
• (countable) Anything foreign that is included in a material,
• (countable, mineralogy) Any material that is trapped inside a mineral during its formation, as a defect in a precious stone.
• (cytology) A nuclear or cytoplasmic aggregate of stainable substances.
• (histology) An object completely inside a tissue, such as epidermal inclusion cyst, a cyst in the epidermis.
• (mathematics) A mapping where the domain is a subset of the image.
• (obsolete) Restriction; limitation.