This is the 68th most frequent Russian word.
тысяч
The Russian word "тысяч" means "thousands" (genitive plural of "тысяча").
'Тысяч' is used in the genitive plural form to indicate an unspecified large number of years.
Прошло уже тысяч лет с того момента.
Thousands of years have passed since that moment.
'Тысячами' is used in the instrumental plural form demonstrating a means or manner, in this case, what the person possesses.
Человек, обладающий тысячами талантов, достоин восхищения.
A person possessing thousands of talents is worthy of admiration.
'Тысячи' is used here in the genitive singular form to mean 'thousand', indicating a specific number above 1000 in relation to the noun 'guests'.