Lengthen rhymes with:
strengthen, strengthen, anthon, blethen, bothun, brethen, cauthen, cauthon, cawthon, donathan, dothan, earthen, elizabethan, ethan, johnathan, johnathon, jonathan, jonathon, jonothan, kathan, lathan, lathon, laythan, lecithin, leviathan, louthan, mathan, mcclenathan, mcglothen, mcglothin, mckeithan, mckeithen, mckethan, midthun, mithun, mothon, nathan, pathan, ramthun, snethen, strengthen, swaminathan, trefethen, trevathan, warthen, wathen, witthuhn, worthen
Lengthen sounds like:
lamston, langdon, langston, langton, lansdown, lansdowne, lanston, lenington, limestone, loewenstein, longden, longtime, longtin, longton, lowenstein, lumsden, lunchtime