
Accumulate
Time Duration
 Use 'accumulate' to show that something is increasing over a period of time, not instantly. 
Over the years, he accumulated a vast collection of stamps.
 Not Always Positive
 'Accumulate' can refer to both desirable and undesirable increases, such as debts or problems. 
They accumulated a lot of debt after buying the house.
 Subtle Growth
 The process of accumulating is often subtle and not easily noticed until it's significant. 
I didn't realize how much clutter I had accumulated over the years.