square meal

 square meal

n.
A substantial, nourishing meal.

A square meal

Meaning

A substantial, nourishing meal.

Origin

It is frequently repeated, by tour guides and the like, that the expression 'a square meal' originated from the Royal Navy practice of serving meals on square wooden plates. Such plates did exist so that is a plausible story, but there's no other evidence to support it. In fact, the lateness of the first printed record (see below) pretty well rules this out as a credible theory. The Royal Navy's records and many thousands of ship's logs are still available and, if the phrase came from that source, it would surely have been recorded before the mid-19th century.
This 'square plate' theory is one of the best-known examples of folk-etymology. The phrase exists, the square plates exist, and two and two make five. To be more precise, what we have here is a back-formation. Someone hears the phrase 'square meal' and then invents a plausible story to fit it.
The word square has many meanings, including 'proper, honest, straightforward', and that's the meaning in 'square meal'. This isn't a rectilinear meal on right-angled crockery, but a good and satisfying meal.
The phrase is of US origin. All the early citations are from America, including this, the earliest print reference I have found - an advertisement for the Hope and Neptune restaurant, in the California newspaper The Mountain Democrat, November 1856:

"We can promise all who patronize us that they can always get a hearty welcome and 'square meal' at the 'Hope and Neptune. Oyster, chicken and game suppers prepared at short notice."

William Brohaugh, in the usually reliable 'English Through the Ages', dates the saying as having entered the language in 1840, although no supporting evidence is provided. There certainly was a spate of coinages of 'food words' in the USA around that date. The terms below all originated in the 1830s and 40s:

Chili con carne
Clambake
Cottage cheese 
Cupcake
Gazpacho
Jerky
Restaurant
Tea cake
Tenderloin 
Tutti-frutti
Seafood

The use of 'square' to mean honest and straightforward goes back to at least the 16th century; for example, in 1591, in Robert Greene's Defence of Conny Catching:

"For feare of trouble I was fain to try my good hap at square play."

Soon after that, Shakespeare used it in Anthony and Cleopatra, 1606:

"She's a most triumphant Lady, if report be square to her."

Other phrases use the word with that same meaning, for example, 'fair and square', 'square play', square deal' etc. but these haven't had spurious derivations invented for them. Coincidentally, another phrase - the opposite of 'fair and square' - also has a false derivation relating to plates in the Royal Navy. The story goes like this. The square wooden plates that sailors received their food on had raised edges called 'fiddles'. If they took too much they were 'on the fiddle'. Perhaps 'story' is being too kind; invention might be more accurate. The evidence for the prosecution is:

- There is no record of the edges of sailors' plates having any name, let alone a fiddle. No dictionary I can find lists that meaning. 
- Despite searching high and low, I've not been able to find any citation of the phrase 'on the fiddle' from before the 20th century, apart from those that clearly mean 'playing the violin'. There are several old 'fiddle' phrases - 'fiddle faddle', 'fiddling while Rome burns', 'second fiddle' etc., but no 'on the fiddle'.

In support of the story there is - well, nothing. It's never possible to prove a negative so, if you hear that derivation from a tour guide and ask for evidence they might just provide it. Don't bet the mortgage on it though; you're more likely to spot Elvis playing tiddlywinks with Lord Lucan.
See other phrases and sayings from Shakespeare.
See other phrases that were coined in the USA.