The phrase "complete blank" means that someone's mind is completely empty or they cannot remember or think of anything at all.
Sentences with «complete blank»
While these characters aren't complete blank slates, it's not unrealistic to assume these are complete strangers to readers. (coreyblake.com)
The Ikariada [1999] 2 Lloyd's Rep 365: first reported case to consider whether failure to complete the blanks on a Congenbill bill of lading can give rise to a claim for damages or an indemnity under a Gencon form of charter. (st-philipsstone.com)
Spelling practice at the KS2 level with National Curriculum spelling words, practising words with «ie» and «ei» spellings Resource includes 3 worksheets to practice 20 words: 1 - look, cover, write for words with «ei» 2 - look, cover, write for words with «ie» 3 - complete the blanks with «ie» or «ei, all 20 words mixed up (tes.com)