had

verb2

1. •
   Used to form the past perfect tense, expressing an action that took place prior to a reference point that is itself in the past.

   • I felt sure that I had seen him before.
   • When I'd (already) done some exercise, I had a cappuccino.
2. •
   As past subjunctive: would have.

   • Had I not known you were coming this evening, I'd have left at midday.