certain A2

/ˈsɝ.tən/ Completely sure that something is true.

certainty B1

/ˈsɝtn̩ti/ The feeling of being completely sure about something.

ascertain B2

/ˌæsɚˈteɪn/ to learn or discover with certainty

certitude C2+

/ˈsɝtɪˌtud/ absolute certainty or conviction

unascertained C2+

/ˌʌnæsɚˈteɪnd/ not yet determined or established with certainty

uncertainly C2+

/ʌnˈsɜːrtənli/ in a hesitant or doubtful manner

uncertainness C2+

/ʌnˈsɜːrtənnəs/ the state of being unsure or doubtful; uncertainty