*yeug-

c. 1300, "unite (something to something else), ally" (a sense now obsolete); late 14c. as "be contiguous with, be adjacent to," from Old French ajoin- stem of ajoindre "join together, unite," from Latin adiungere "fasten on, harness, join to," from ad "to" (see ad-) + iungere "to bind together" (from a nasalized form of PIE root *yeug- "to join"). The meaning "be contiguous with, be in contact with" is from late 14c. The French word was Latinized 16c. to Modern French adjoindre. Related: Adjoined; adjoining.

late 14c., ajusten, "to correct, remedy," from Old French ajuster, ajoster "add; assemble; calibrate, gauge, regulate," from Late Latin adiuxtare "to bring near," from ad "to" (see ad-) + Latin iuxta "next, close by" (from suffixed form of PIE root *yeug- "to join").

In 16c. French corrected to adjuster, but the pedantic effort was rejected and Modern French has ajouter. Influenced in form and sense by folk-etymology, as if from ad- + iustus "just, equitable, fair."

English reborrowed the word by c. 1600 in sense "arrange, settle, compose," from French adjuster "fit (things together) properly, put things in order." The meaning "arrange (something) so as to conform with (a standard or another thing)" is from 1660s. The insurance sense is from 1755 (see adjuster). To adjust to "get used to" is attested by 1924. Related: Adjusted; adjusting.