Here's what rhymes with sweetening.

Consider these alternatives

sweeten / region flavoring / favoring sweetens / regions emulsifying / dying flavouring / favoring diluting / including tempering / entering lactulose / close treasuring / measuring antihypertensive / extensive spurns / terms borate / late palatability / ability pharmacologic / logic cooly / newly piperidine / seen forgoing / going rediscovering / covering purifying / dying barium / ovarian