Inseparable

google

ref

late Middle English: from Latin inseparabilis, from in- ‘not’ + separabilis (see separable).

wiktionary

ref

From Middle English, from Middle French inséparable, from Latin īnsēparābilis. Constructed as in- +‎ separable.

etymonline

ref

inseparable (adj.)

mid-14c., from Latin inseparabilis "that cannot be separated," from in- "not, opposite of" (see in- (1)) + separabilis, from separare "to pull apart" (see separate (v.)). Related: Inseparably.