Real Dictionary

-istic in American English
of or relating to an action, practice, doctrine, quality, etc., or to a person involved in or with it
suffix: a suffix of adjectives (and in the plural, of nouns from adjectives) formed from nouns ending in -ist and having reference to such nouns, or to associated nouns in -ism (deistic; euphuistic; puristic). In nouns, it usually has a plural form (linguistics)

-istic in British English
suffix forming adjectives: equivalent to a combination of -ist and -ic but in some words having a less specific or literal application and sometimes a mildly pejorative force, as compared with corresponding adjectives ending in -ist