"slice or small bulb forming together a large bulb, as of garlic," Old English clufu "clove (of garlic), bulb, tuber," from Proto-Germanic *klubo "cleft, thing cloven" (source also of Old High German chlobo, Old Norse klofi), from PIE root *gleubh- "to tear apart, cleave."
Its Germanic cognates mostly lurk in compounds that translate as "clove-leek," such as Old Saxon clufloc, Old High German chlobilouh. Dissimilation produced Dutch knoflook, German Knoblauch.