What is the meaning of speculate?

verb

• To believe especially on uncertain or tentative grounds.
  • usage: "Scientists supposed that large dinosaurs lived in swamps"
  • synonyms: theorize, theorise, conjecture, hypothesize, hypothesise, hypothecate, suppose
• Talk over conjecturally, or review in an idle or casual way and with an element of doubt or without sufficient reason to reach a conclusion.
  • usage: "We were speculating whether the President had to resign after the scandal"
• Reflect deeply on a subject.
  • usage: "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, think over, meditate, ponder, excogitate, contemplate, muse, reflect, mull, mull over, ruminate
• Invest at a risk.
  • usage: "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