Myriad: Ten thousand. A myriad can also mean: an immense number.
We English speakers tend to use myriad to talk about something innumerable. For example, I ran across myriad this week while reading The Story of English by the Roberts McCrum and MacNeil.
“All one can say with confidence in the year 2001 is that, as participants in global English, in all its myriad manifestations, we are probably closer in spirit and self-expression to the Elizabethan linguistic extravaganza than at any time since the early 17th century.”
Myriad comes from the Greek word myrias (μυριάs) meaning countless, or ten thousand (which is, to me, a bit ironic).
I can’t give you a myriad of synonyms. So, here are a few: countless, endless, heaps, lots, multiple, and scad.