"Goumin, a pet-services portal, says China has 73.5m cat- or dog-owners, a group approaching the size of the 90m-strong Communist Party." What does "90m-strong" mean here? Thanks.
10 feet long = ten feet in length
10 feet high = ten feet in height
10 feet wide = ten feet in width
10 feet deep = ten feet in depth
10 inches thick = 10 inches in thickness
a million strong = a million in strength
And the "strength" of a group is normally expressed in how many individuals it contains.
An army 10,000 strong marched on the city.
90m is an abbreviation for 90 million.
So "the 90m-strong Communist Party" means "the Communist Party, which has 90 million members". Note that the hyphen is unusual; normally one would just write "90m strong".
Strength here implies size, as it does for the thickness of wooden boards, where the strength is significantly depending on size. Some words for crowds, and people, like e.g. German deutsch, are supposed to be from a root meaning strength. Also compare string (for the audible similarity) vs band and bond, for example. Also compare mighty.
And 90 m means ninety million.