The term 'develop gradually' can be summarized by two crossword solutions: gestate (7 letters) and EVOLVE (6 letters). Gestate is a verb meaning to develop or grow slowly, often in reference to a fetus in the womb. EVOLVE is a verb meaning to gradually change over time, often in reference to species adapting to their environment. Both words imply a gradual process of development, making them suitable solutions for the term 'develop gradually'.