This is one of those words that divides the English language – in British English it is a crumbly oatmeal dessert, while in the US it means “pancake”.
And it seems that the meaning of the word as it is known in the US is in fact the original sense, and it is in the UK that the word has evolved.
The word is made up of two elements: flap + jack. We might use it differently today, but one meaning of “flap”, dating from the 1300s, is “flip”, as you would a pancake, or “toss with a quick movement”.
The second element, “jack”, presents something of a problem. There are of course a number of English words that use “jack” as a suffix – lumberjack, skipjack, natterjack, steeplejack, etc. But none of the senses really seem to apply to “flapjack”. One theory I have come across is that it might be a reference to size, as one meaning of jack is “fairly small”.
Now let’s take a look at the compound word. “Flapjack” has been in use since the early 17th century. But at that time it seems to have either meant a kind of flat apple tart (apple-jack) or a pancake (also flat, of course!).
Interestingly, the play Pericles, Prince of Tyre, which is at least in part attributed to Shakespeare, although there is some dispute about this, contains a reference to “flapjack”. It can be found in Act II Scene I, where the First Fisherman says to Pericles:
Come, thou shalt go home, and
we’ll have flesh for holidays, fish for
fasting-days, and moreo’er puddings and flap-jacks,
and thou shalt be welcome.
In British English, the “pancake” or “apple tart” meaning for “flapjack” has largely been lost, and it is now mostly used to refer to the oatmeal cakes as in the picture, while in the US, the “pancake” meaning has remained. However, British English speakers might be surprised to learn that the “oatmeal cake” usage is a fairly recent coinage, and dates only to the 1930s.