A Great/large Number and a great/large quantity are synonyms for multitude. Handful is the opposite of multitude. We have given below a collection of synonyms for "multitude".
A 'Multitude' means a large number, but its secondary meaning is a large gathering of people. It is a group of people. Because a group is a singular concept, It cannot be counted. For example, the President addressed a large number of people. Beware of the crowds using the streets while giving thanks.