Pertaining to, or designating, a verb which forms its
   preterit (imperfect) by a variation in the root vowel, and the past
   participle (usually) by the addition of -en (with or without a change
   of the root vowel); as in the verbs strive, strove, striven; break,
   broke, broken; drink, drank, drunk. Opposed to weak, or regular. See
   Weak.