Straightening rhymes with:
battening, brightening, captaining, disheartening, enlightening, fattening, flattening, frightening, heartening, heightening, lightening, shortening, smartening, sweetening, threatening, tightening
battening, brightening, captaining, disheartening, enlightening, fattening, flattening, frightening, heartening, heightening, lightening, shortening, smartening, sweetening, threatening, tightening