1. A small familiar blanket or other soft fabric item carried by a child for reassurance.
2. A form of harness for a baby's crib.
3. All-encompassing military and political security measures.
The term 'security blanket', also known as 'comfort blanket', was coined by Charles Schulz for his Peanuts cartoon strip. That's what most references will tell you. It's always a pleasure to swim against the tide and here's an opportunity. In fact, the term 'security blanket' wasn't coined by Charles Schulz for his Peanuts cartoon strip. The derivation of 'security blanket' involves a rather meandering tale, which goes like this:
Security blankets were known to Americans in the 1920s and were at that date overblankets which were clipped into babies' cribs to stop the occupants falling out. The accompanying advert is from the New York newspaper The Republican Press, November 1925, advertising fasteners for such a blanket for 59 cents.
The tale now moves on to World War II. The term 'security blanket' was then used to refer to strict security measures that were taken to keep Allied military plans from falling into the hands of the Germans. The term was coined in that context by the US military while fighting in Europe. For example, this report from the Alabama newspaper The Dothan Eagle, September 1944:
Reports being issued at Gen. Dwight D. Eisenhower's headquarters sometimes were as much as 48 hours behind the armies because of a security blanket thrown over the operations.
Incidentally, another article from the same page as the above is titled 'British Take Brussels', which is timely as this [28th December] is the only week of the year that the headline could be recycled. For those of a non-British persuasion, many in Britain pile their Christmas dinner plates with brussels sprouts with some enthusiasm but reject them with distaste for the rest of the year.
The emergence of the military use of 'security blanket' about twenty years after the use of the term in a domestic setting does suggest the possibility that those coining a new meaning for it were the babies that were tucked up under security blankets a generation earlier.
Now we move on another step, to the use of the expression as 'a small familiar comforter for babies and toddlers'. Now we get to Charles Schulz, right? Not quite. Schulz drew the character Linus van Pelt with a comfort blanket in the Peanuts cartoon strip in June 1954. It wasn't until 1956, in Good Grief, More Peanuts, that the item was given a name by Linus:
"This is a 'security and happiness' blanket. All little kids carry them."
By that date the term had been in use elsewhere. The November 1954 issue of the California newspaper The Daily Review included this piece by a staff writer, under the name of 'Bev':
'Security blanket. My younger child is one year old. When she finds a fuzzy blanket or a fleecy coat she presses her cheek against it and sucks her thumb.'
See other phrases that were coined in the USA.