The term ACORN SOURCE is composed of two words, OAK and OAKTREE. OAK is a three-letter word that refers to a type of tree that is native to the Northern Hemisphere and is found in many temperate and subtropical regions. OAKTREE is a seven-letter word that refers to a large, deciduous tree that is often used for timber and is known for its acorns, which are a type of nut. Acorns are an important source of food for many animals, including squirrels, birds, and deer.