1
general::
Obliterate, wipe out of existence or memory, as in At least one Indian nation was blotted out as the pioneers moved west, or The trauma of the accident blotted out all her memory of recent events. This idiom, first recorded in 1516, uses the verb to blot in the sense of making something illegible by spotting or staining it with ink. The New Testament has it (Acts 3:19): "Repent ye . . . that your sins may be blotted out."
American Heritage Idioms
2
general::
Phrase(s): blot someone out
Sl. to kill someone. (Originally underworld slang.) • Sorry, chum, we got orders to blot you out. • The gang blotted out the only living witness before the trial., Phrase(s): blot someone or something out
Fig. to forget someone or something by covering up memories or by trying to forget. • I try to blot those bad thoughts out. • I tried to blot out those unhappy days., Phrase(s): blot something out
to make something invisible by covering it. (See also blot someone or something out.) • Don’t blot the name out on the application form. • Who blotted out the name on this form?
McGrawhill's American Idioms And Phrasal Verbs