Speculation rhymes with:
articulation, calculation, innoculation, inoculation, miscalculation, recalculation, accumulation, articulation, calculation, coagulation, confabulation, deregulation, emulation, formulation, granulation, innoculation, inoculation, manipulation, miscalculation, overpopulation, overregulation, ovulation, population, recalculation, regulation, reregulation, simulation, stimulation, stipulation, strangulation, tabulation, tribulation