A focal growth that resembles a neoplasm but results from faulty development in an organ WordNet 3.0 & Open English WordNet

A hamartoma is a mostly benign, local malformation of cells that resembles a neoplasm of local tissue but is usually due to an overgrowth of multiple aberrant cells, with a basis in a systemic genetic condition, rather than a growth descended from a single mutated cell, as would typically define a benign neoplasm/tumor. Wikipedia

Non-cancerous growth, made up of an abnormal mixture of cells and tissues normally found in the area of the body Wikidata