ETYM Pref. un- + certain. Related to Incertain.
1. Lacking or indicating lack of confidence or assurance; SYN. unsure, incertain.
2. Not established beyond doubt; still undecided or unknown.
3. Not certain to occur; not inevitable.
4. Not consistent or dependable.
5. Not firm or secure.
6. Not safe from danger or mishap; SYN. unsure.
7. Especially in the negative as in, meaning.