ETYM Latin subjunctivus, from subjungere, subjunctum, to subjoin: cf. French subjonctif. Related to Subjoin.
(Grammar) Relating to a mood of verbs.

The subjunctive mood; also, a verb in the subjunctive mood.
Grammar, (pertaining to) mood of verb expressing possibility, desire, etc., and not actuality or fact.
In grammar, the mood of the verb in a sentence that expresses a wish, a condition, or an assumption. In English, the subjunctive occurs mainly in certain phrases such as “i wish I were”, “if it were so”, “far be it from me”, “God bless”.
The subjunctive mood is marked by the form of the verb—“i were” and “he were”. The use of was in the first two examples is an acceptable alternative.