c. 1300, poumgarnet (a metathesized form), "the large, roundish, many-seeded, red-pulped fruit of the pomegranate tree," from Old French pome grenate (Modern French grenade) and directly from Medieval Latin pomum granatum, literally "apple with many seeds," from pome "apple; fruit" (see Pomona) + grenate "having grains," from Latin granata, fem. of granatus, from granum "grain" (from PIE root *gre-no- "grain").
The classical Latin name was mālum granatum "seeded apple" or mālum Punicum "Punic apple." Italian form is granata, Spanish is granada. The -gra- spelling was restored in English early 15c. Of the tree itself from late 14c.