IPA: /ɪnˈfɜːrməri/
KK: /ɪnˈfɜrməˌri/
A place where people who are sick or injured receive medical care, often found in schools, military bases, or other institutions.
The students went to the infirmary to get treatment for their colds.
Infirmary → It is formed from "infirmus" (from Latin, meaning weak or ill) and the suffix "-ary" (meaning relating to or connected with). An infirmary is a place related to the care of the weak or ill.
Think of a place that is 'related to' ('-ary') caring for those who are 'weak' ('infirmus') — that's what an infirmary is.