1) Gradually built up 2) Growing by accretion 3) Increasing 
• (a.) Relating to accretion; increasing, or adding to, by growth.
If a company acquires another and says the deal is 'accretive to earnings', it means that the result
Ac·cre'tive adjective Relating to accretion; increasing, or adding to, by growth. Glanvill. 
[adj] - growing by accretion
adjective growing by accretion