เลย turns up constantly and means something different almost every time. Its root sense is going past a point, and the rest follow from that: after a verb it hands over permission — กินเลย, go ahead and eat; wrapped in ไม่ … เลย it means not at all; in directions it means carry on, don't stop; and on the end of a remark it turns it up — สูงมากเลย, really tall. Learn the root and they stop looking like separate words.