Blocking

Blocking is a process assumed in Aronoff (1976) by which the existence of one word, which is listed in the mental dictionary, prevents the application of an unproductive word formation rule, if that application would give rise to a complex word having the same semantics as the already existing word.

Examples
The English suffixes -ity and -ness are very similar, the difference being that the former is unproductive and the latter productive. Both can be added to adjectives ending in -ous (curious: curiosity: curiousness). However, if there already exists a noun corresponding to the adjective in -ous as in the case of glorious: glory, gracious: grace, furious: fury etc., -ity affixation, but not -ness affixation, is disallowed: *gloriosity: gloriousness, *graciosity: graciousness, and *furiosity: furiousness.

Link
Utrecht Lexicon of Linguistics