Make sure, you have proper db, table and column charset/collation in your database. When table is created in database, it relies on environmental settings, so if you have charset/collation set for DB that doesn’t allow special characters by default (utf8 characters), then the results will be wrong.
Should be: charset – utf8, collation – utf8_general_ci.
Try following SQL Queries (replace your_wp_db_name with the database name you have set in your WordPress installation):
ALTER DATABASE your_wp_db_name DEFAULT CHARACTER SET utf8 DEFAULT COLLATE utf8_general_ci;
ALTER TABLE your_wp_db_name.wp_glossary_synonyms MODIFY synonym VARCHAR(145) CHARACTER SET utf8 COLLATE utf8_general_ci;
Make sure the Terms are defined to not be case-sensitive in setting page.