Syntinen Laulu posted this question at Wordorigins.org:
I can’t find that this has been discussed here before: in what sense is high tea ‘high’? This puzzled me when I was a child, and I’ve never heard it convincingly explained.
Dave Wilton, who runs the site, gave what is apparently the best answer that can be given:
The OED provides no clue, simply listing high tea with other high phrases.
My guess is that it would fall into the OED’s sense at high, adj. and n.2, 16: “Of a time of day or season (esp. summer): well advanced; fully come, complete. Cf. HIGH DAY n.1 2, HIGH NOON n. 1, high season n.” There is also the high Renaissance and the high Middle Ages.
High tea itself is technically not a time or period, but it’s closely associated with a particular time of day.
There followed a discussion of what exactly “high tea” is that surprised and enlightened me; it’s “sometimes known as meat tea,” and:
[…] anyone in the Southeast [of England] who:
(a) calls their midday meal ‘dinner’,
(b) expects to eat their evening meal fairly soon after returning home from work or school,
(c) drinks no beer or wine with it,
– generally calls their evening meal their ‘tea’; even though as often or not they don’t drink any tea with it.
You can have tea without tea! Furthermore, “I have been told that many Leftpondians understand ‘high tea’ to mean ‘olde Englishe posh afternoon tea à la Downton Abbey’, and that overpriced hotels and tea shops courting the tourist trade accordingly advertise their afternoon teas as ‘high tea’.” Absolutely true, and that was how I had understood it.
Any further information or anecdotes welcome, as always.