mid-15c., secluden, transitive, "to cut off from, shut or keep out" (implied in ben secluded), a sense now archaic, from Latin secludere "shut off, confine," from se- "apart" (see se-) + -cludere, variant of claudere "to shut" (see close (v.)). The meaning "remove or guard from public view" is recorded from 1620s. Related: Secluded; secluding.
word-forming element making adjectives from verbs, meaning "pertaining to, tending to; doing, serving to do," in some cases from Old French -if, but usually directly from Latin adjectival suffix -ivus (source also of Italian and Spanish -ivo). In some words borrowed from French at an early date it has been reduced to -y (as in hasty, tardy).
<a href="https://www.etymonline.com/word/seclusive">Etymology of seclusive by etymonline</a>
Harper, D. (n.d.). Etymology of seclusive. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/seclusive