Here's what rhymes with meaningful.

Consider these alternatives

constructive / destructive significant / insignificant achieve / leave worthwhile / while dialogue / talk measurable / preferable substantial / sample realistic / characteristic productive / destructive achieving / leaving necessary / very truly / newly any / many comprehensive / extensive make / take opportunity / unity objective / effective engage / stage prove / use reasonable / treasonable realize / realise satisfying / dying initiate / state anything / him indeed / need crucial / removal