causeless

adj

1. Having no obvious cause; fortuitous or inexplicable.
2. Groundless or unreasonable.

   “[H]e […] by his overcarefulneſſe and cauſeleſſe ſuſpicion, deprived himſelf of this benefit, and implunged himſelf in much juſt hatred for his unjuſt dealing and treachery.”

   “Alas my fears are cauſless, and ungrounded, / Fantaſtick dreams, and melancholick fumes / Of crazy ſtomacks, and diſtempered brains: / Has this convinc'd you?”