unprepossessing

un- +‎ prepossessing

unprepossessing (comparative more unprepossessing, superlative most unprepossessing)

1. Unimpressive or unremarkable; dull and ordinary; nondescript.
   • 1838, Nathaniel Hawthorne, "Sylph Etherege":

     One of these unseen observers, a gentleman, was youthful, and had an air of high breeding and refinement, and a face marked with intellect, though otherwise of unprepossessing aspect.

   • 1902, Myrtle Reed, At the Sign of the Jack O'Lantern, ch. 4:

     She drew up a chamois-skin bag, of an unprepossessing mouse colour, and emptied out a roll of bills.

   • 2017 Jan. 12, Andy Webster, "Movie Review: Horses Under the Hood?," New York Times (retrieved 15 Jan 2017):

     Sometimes movies with the most unprepossessing titles can surprise you. Case in point: “Monster Trucks,” a spry, spirited and delightful family film.