believe

From Middle English beleven, bileven, from Old English belīefan (“to believe”), from Proto-West Germanic *bilaubijan (“to believe”), equivalent to be- +‎ leave (“to give leave or permission to, permit, allow, grant”). Cognate with Scots beleve (“to believe”), Old Frisian bilēva (“to permit”), Middle Dutch beloven (“to believe, entrust”), Middle Low German belö̂ven (“to believe”), Middle High German belouben (“to believe”).

A related term in Old English was ġelīefan (“to be dear to; believe, trust”), from Proto-West Germanic *galaubijan (“to have faith, believe”), from Proto-Germanic *galaubijaną. Compare also Old English ġelēafa (“belief, faith, confidence, trust”), Old English lēof ("dear, valued, beloved, pleasant, agreeable" > English lief). Related also to North Frisian leauwjen (“to believe”), Saterland Frisian leeuwe (“to believe”), West Frisian leauwe (“to believe”), Dutch geloven (“to believe”), German Low German glöven (“to believe”), German glauben (“to believe”), Gothic 𐌲𐌰𐌻𐌰𐌿𐌱𐌾𐌰𐌽 (galaubjan, “to hold dear, valuable, or satisfactory, approve of, believe”).

The prepositionally transitive senses with in are a semantic loan from Latin crēdō in aliquem / aliquid.