Diagram rhymes with:
anagram, centigram, electrocardiogram, epigram, histogram, hologram, kilogram, logogram, milligram, monogram, sonogram, telegram
Diagram sounds like:
dacron, decorum, decrane, degarmo, deguerin, dekroon, dezarn, dezern, dickerman, digeronimo, disarm, discern, disharmony, disharoon, ducharme