Productivity

Productivity is a term which mainly applies to word formation processes. If a process is fully regular and actively used in the creation of new words, one regards this process as being productive. Productive word formation is opposed to unproductive word formation.

Examples
The English suffix -ness can be attached to any adjective even if there is a more conventionally acceptable alternative (sterileness next to sterility). We say that -ness is a productive suffix. We can contrast this with the suffix -th which performs the same role, but only for a handful of words (sometimes accompanied by other idiosyncratic changes): warmth, strength, health. The suffix -th is unproductive. Linguists differ in the way productivity is treated. Many linguists (e.g. Aronoff 1976) take the position that linguistic theory must account for differences in productivity, while others (e.g. DiSciullo &amp; Williams 1987) assume that productivity is a matter of performance, and must be explained elsewhere.

Links
Utrecht Lexicon of Linguistics