IPA: /ɪnˈfɪnɪtjuːd/
KK: /ɪnˈfɪnɪˌtud/
A very large or unlimited amount or number of something.
The universe is filled with an infinitude of stars and galaxies.
Infinitude is formed from "in-" (meaning not) and "finitus" (from Latin, meaning limited or finite) and the suffix "-ude" (indicating a state or condition). The word describes a state of being not limited, or boundless, hence referring to infinity.
Think of 'not limited' ('in-') and 'finite' ('finitus') to remember that 'infinitude' means a state of being boundless or infinite.