means To shine with small, bright, dancing flashes of reflected light — or, of a person, to be lively and brilliantly charming.

from From Middle English 'sparklen,' a frequentative of 'sparken' — to give off sparks. The little '-le' ending does what it usually does in English: turns one action into a flickering repetition, the way 'twink' becomes 'twinkle' and 'crack' becomes 'crackle.' So a sparkle is, quite literally, the verb 'spark' caught in the act of doing it over and over. 'Spark' itself goes back to Old English 'spearca,' with cousins across the old Germanic tongues, all describing the bright flecks that leap from a fire.