sure

Concise Oxford English Dictionary © 2008 Oxford University Press:
sure /ʃɔː, ʃʊə/

▶adjective

• 1 completely confident that one is right.

• 2 (sure of/to do something) certain to receive, get, or do something.

• 3 undoubtedly true; completely reliable.

• 4 confident or assured.

▶adverb [often as exclam.] informal, chiefly N. Amer. certainly.

– phrases
be sure [usu. in imper.] do not fail.
for sure informal without doubt.
make sure confirm or ensure.
sure enough informal used to introduce a statement that confirms something previously predicted.
sure thing informal a certainty.

■ [as exclam.] chiefly N. Amer. certainly.

to be sure certainly; it must be admitted.

– derivatives
sureness noun.

– origin ME: from OFr. sur, from L. securus ‘free from care’.