bit_by_bit
1. [ adverb ] a little bit at a time
Synonyms: little_by_little in_stages piecemeal
Examples:

"the research structure has developed piecemeal"

2. [ adverb ] in a gradual manner
Synonyms: gradually step_by_step
Examples:

"the snake moved gradually toward its victim"

Related terms: gradual gradual
Similar spelling:   bit-by-bit