c. 1500, "characteristic of one who is submissive or obedient," from Late Latin subiectivus "of the subject, subjective," from subiectus "lying under, below, near bordering on," figuratively "subjected, subdued"(see subject (n.)). In early Modern English as "existing, real;" more restricted meaning "existing in the mind" (the mind as "the thinking subject") is from 1707, popularized by Kant and his contemporaries; thus, in art and literature, "personal, idiosyncratic" (1767). Related: Subjectively; subjectiveness.
word-forming element making abstract nouns from adjectives and meaning "condition or quality of being ______," from Middle English -ite, from Old French -ete (Modern French -ité) and directly from Latin -itatem (nominative -itas), suffix denoting state or condition, composed of -i- (from the stem or else a connective) + the common abstract suffix -tas (see -ty (2)).
Roughly, the word in -ity usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances; & the word in -ism means the disposition, or collectively all those who feel it. [Fowler]
<a href="https://www.etymonline.com/word/subjectivity">Etymology of subjectivity by etymonline</a>
Harper, D. (n.d.). Etymology of subjectivity. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/subjectivity