Example : Let us say that he did not tell the truth.
Let's say you had a lot of money--what would you do?.

Synonyms : say

Example : I imagine she earned a lot of money with her new novel.
I thought to find her in a bad state.
He didn't think to find her in the kitchen.
I guess she is angry at me for standing her up.

Synonyms : guess, imagine, opine, reckon, think

Example : Scientists supposed that large dinosaurs lived in swamps.

Synonyms : conjecture, hypothecate, hypothesise, hypothesize, speculate, theorise, theorize

Example : I presuppose that you have done your work.

Synonyms : presuppose

Example : This step presupposes two prior ones.

Synonyms : presuppose