Accumulate, amass and hoard imply in both literal and figurative usage a bringing together so as to make a store or great quantity.
Accumulate implies a piling up by a series of increases rather than by a single complete act; it is applicable to almost anything that may increase in amount.
- unused books accumulate dust
- he will ever be gathering knowledge, accumulating experience, as he can
- true poetry, however simple it may appear on the surface, accumulates meaning every time it is read
Amass refers usually but not always to things that are regarded as valuable, such as money or treasures.
- amass a fortune
It frequently implies more imposing results than accumulate.
- scientific knowledge, painstakingly amassed by many devotees over an extended period of human history
Hoard always implies storing up and frequently concealment of what is stored.
- squirrels hoard nuts for the winter months
Frequently hoard implies greed and, when used of money, avarice.
- a miser is one who hoards gold
- hoarding money is not a safe way of saving