Common words that rhyme with ascertain include certain, entertain, appertain, sustain, retain, obtain, attain, mountain, refrain, plain, drain, birdbrain, bargain, ordain and blockchain.
I am certain about this.
Seek guidance when feeling uncertain.
She told a made-up story to entertain the kids.
The acid left a stain on the metal.
Trees help sustain life on Earth.
She struggles to maintain balance.