Because the disease name isn’t a plural of scleros.
Sclerosis (from the greek skleros meaning hard) is the stiffening of tissue.
i think they know that. if you pluralized ‘sclerosis’, you’d expect to get ‘scleroses’. just like pluralizing ‘thrombosis’ gets you ‘thromboses’.
The disease isn’t a plural. Which i already said.
Scleroses would translate as “hardening diseases” though. There’s only one disease.
osis meaning a disease
Just as additional info: this is correct for English. In Ancient Greek the suffix -ωσις/-ōsis is wider, basically “plop it on a verb to get a noun for process, action or result”; so it’s a lot like one of English -ing suffixes (the one that makes nouns from verbs). e.g.
- the falling = πτῶσις/ptôsis
- the seizing = ἅλωσῐς/hálōsis
Because that “multiple” doesn’t refer to multiple hardening (σκλήρωσῐς/sklḗrōsis) events, but rather to hardening as something uncountable happening in multiple spots.
It’s roughly “multiple hardening”, note how the lack of a plural doesn’t feel off in this one either.
For reference, in languages showing adjective-noun agreement, the adjective gets the singular (e.g. Portuguese “esclerose múltipla” - the plural would be “escleroses múltiplas”).
