It is quite absurd to claim that Marx did not know that word. Although, in his most important writings the exact letter sequence is indeed not recorded. For example: It is not in the German version of the first edition of the first volume of Das Kapital In lesser known works — it is present.
It was a prominent word used by economist David Ricardo which Marx ...
LаngLаngС found that:
"Kapitalismus" does not appear in the German version of Das Kapital Bd. I.
It does appear in Das Kapital Bd. II published from Marx's notes after Marx's death.
It does appear in Marx's other notes and letters after 1877.
Lunchonacho additionally found that:
It does appear in multiple places in the 1872 edition.
It appears in the ...
I had a look at the etymology of capitalism and, according to Wikipedia:
The initial usage of the term capitalism in its modern sense has been attributed to Louis Blanc in 1850 and Pierre-Joseph Proudhon in 1861. Karl Marx and Friedrich Engels referred to the capitalistic system (kapitalistisches System) and to the capitalist mode of production (...