productive

In morphology (the linguistics kind), productivity is a potential property of word formation rules, namely, the rule being able to be used to create new words, not listed in any dictionary or previously encountered by the speaker.

An example: the suffix -ish, used to create adjectives out of adjectives.
I can talk about something greatish before an audience that has never encountered that word - they may smile, but they will understand what I mean. I may even encounter an adjective I've never seen before in my life and instantly apply -ish to it to form a new adjective, and its meaning will be clear to whoever understands the meaning of the original adjective.

Pro*duc"tive (?), a. [F. productif, L. productivus fit for prolongation.]

1.

Having the quality or power of producing; yielding or furnishing results; as, productive soil; productive enterprises; productive labor, that which increases the number or amount of products.

2.

Bringing into being; causing to exist; producing; originative; as, an age productive of great men; a spirit productive of heroic achievements.

And kindle with thy own productive fire. Dryden.

This is turning nobility into a principle of virtue, and making it productive of merit. Spectator.

3.

Producing, or able to produce, in large measure; fertile; profitable.

-- Pro*duc"tive*ly, adv. -- Pro*duc"tive*ness, n.

© Webster 1913.