For certain and Well-grounded

For certain adverb - Definitely or positively (`sure' is sometimes used informally for `surely').

Well-grounded and for certain are semantically related. in definite topic. In some cases you can use "Well-grounded" instead an adjective phrase "For certain".

Well-grounded adjective - According to the rules of logic.

For certain and well-grounded are semantically related. Sometimes you can use "For certain" instead an adjective phrase "Well-grounded".