An Etymological Dictionary of Astronomy and Astrophysics

1. A person who follows or upholds a leader, cause, etc.; supporter; follower.
   

2. Sticking; clinging; adhering (Dictionary.com).

Etymology (EN): From O.Fr. adherent or directly from L. adhaerentem pr.p. of adhaerere “to stick to,” → adhere.

Etymology (PE): Âdusandé, from âdusidan, → adhere.