subjunctive (n.)

"mood employed to denote an action or state as conceived and not as a fact," 1620s, from earlier adjectival use of subjunctive (1520s), from Late Latin subiunctivus "serving to join, connecting," from subiunct-, past participle stem of Latin subiungere "to append, add at the end, place under," from sub "under" (see sub-) + iungere "to join together" (from nasalized form of PIE root *yeug- "to join"). The Latin modus subiunctivus probably is a grammarians' loan-translation of Greek hypotaktike enklisis "subordinated," so called because the Greek subjunctive mood is used almost exclusively in subordinate clauses.