Antonym: perhaps. Similar words: certainly not, certain, uncertain, for certain, uncertainty, entertainment, mainly, ungainly. Meaning: ['sɜːtnlɪ] 
adv. definitely or positively (`sure' is sometimes used informally for `surely').
adv. definitely or positively (`sure' is sometimes used informally for `surely'). 
Random good picture Not show
More similar words: certainly not, certain, uncertain, for certain, uncertainty, entertainment, mainly, ungainly, curtain, maintain, concert, undertake, obtain, retain, sustain, captain, contain, container, retaining, sustainable, in line, only, openly, if only, only too, fall in love, in line with, commonly, only that, cancer.