Summation rhymes with:
approximation, consummation, acclamation, acclimation, amalgamation, animation, approximation, automation, consummation, defamation, estimation, exclamation, inflammation, intimation, proclamation, reclamation
Summation sounds like:
saindon, samedan, sandeen, sanden, sandin, sandino, sandman, sandmann, sandom, sandon, sandtown, sanitation, santana, santayana, santin, santini, santino, santon, santone, santoni, schwendeman, segmentation, sentman, shantytown, shenton, simonton, sindona, sindoni, sinton, smetana, smithtown, smitten, smoothen, snedden, sneddon, snethen, snowden, snowdon, somethin', sometime, sondheim, sumatoma, sumatomo, sumitomo, sundeen, sundheim, sundin, sundown, suntan, swaminathan, swanton, swinton