We were talking about how explaining something to a 10-year-old sometimes means that you use words that a 10-year-old doesn't know. And that a 10-year-old should have the ability to use a dictionary to look up unfamiliar words.

I was also implying that you, and I assumed that you were more than 10 years old, could also use a dictionary to look up words you weren't familiar with if you aren't able to glean their definition from context.

Can a 10-year-old use a dictionary? That's approximately fifth grade in the US. By 10 years old, they should be able to use a dictionary and encyclopedias to look up stuff. At the very least they should be able to go to merriam-webster.com or wherever and type in an unfamiliar word to get a definition.

Could be your sphere of reading and / or age - it's common enough in (say) the British Ripping Yarns genre of boys own colonial adventures.

So UK, Canadian, Australian boys who were ten years old in the 1950s, 1960s, 1970s would have encountered it. Anything that featured older school British Empire toy soldiers would have likely used the word, along with other military terms.

Rudyard Kipling is a typical kind of author who'd be read by ten year olds and who'd use that word and others of a similar pedigree.