the quality of something that causes or assists healthy growth
<noun.attribute>
the intellectual productivity of a creative imagination
<noun.cognition>
Fruitful \Fruit"ful\, a. Full of fruit; producing fruit abundantly; bearing results; prolific; fertile; liberal; bountiful; as, a fruitful tree, or season, or soil; a fruitful wife. -- {Fruit"ful*ly}, adv. -- {Fruit"ful*ness}, n.
Be fruitful and multiply and replenish the earth. --Gen. i. 28.
[Nature] By disburdening grows More fruitful. --Milton.
The great fruitfulness of the poet's fancy. --Addison.