retentionist
/rɪˈtɛnʃ(ə)nɪst/ /rɪˈtɛnʃ(ə)nɪst/noun
1 Generally. A person who advocates the retention of something; a supporter of retention.
2Chiefly historical. A person who advocates the retention of territory, especially the retention by the United States of the Philippines and other Spanish overseas territories annexed during the Spanish-American War (1898).
3A person who advocates the retention of a law or practice; specifically a person who advocates the retention of capital (or occasionally corporal) punishment.
adjective
Of or relating to retentionists; that advocates retention of something.
Origin
Mid 19th century; earliest use found in The Zoologist: a miscellany of natural history. From retention + -ist.