increment
Meaning: an enlargement; the process of increasing
Usage: The workmen made the wall longer, increment by increment.
cumulative
Meaning: increasing, building upon itself
Usage: The cumulative effect of hours spent in the sun was a deep tan.
accretion
Meaning: slow growth in size or amount
Usage: Stalactites are formed by the accretion of minerals from the roofs of caves.
culmination
Meaning: the climax toward which something progresses
Usage: The culmination of the debate was a unanimous class vote.