Example : Scientists supposed that large dinosaurs lived in swamps.

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

Example : We were speculating whether the President had to resign after the scandal.

Example : I mulled over the events of the afternoon.
Philosophers have speculated on the question of God for thousands of years.
The scientist must stop to observe and start to excogitate.

Synonyms : chew over, contemplate, excogitate, meditate, mull, mull over, muse, ponder, reflect, ruminate, think over

Example : I bought this house not because I want to live in it but to sell it later at a good price, so I am speculating.

Synonyms : job