hilly

the word 'hilly' is a native english formation. its core, 'hill', originates from old english 'hyll', a common germanic term for a natural elevation of land. the adjectival suffix '-y', also from old english '-ig', is a highly productive suffix meaning "abounding in" or "having the quality of". therefore, the literal construction "full of hills" directly and transparently conveys its modern meaning, describing terrain characterized by numerous hills. this pattern of attaching '-y' to a noun to create a descriptive adjective is a fundamental and enduring feature of english word formation.

Structure: hill (a naturally raised area of land) + y (adjective-forming suffix) hill (old english, functional role: root, denoting the landform) + y (old english, functional role: suffix, meaning "characterized by" or "full of")