Here’s a context clues worksheet on en route. Merriam-Webster says it can be used as both an adjective and an adverb, but I’ve only used it as an adverb, and I cannot, off the top of my head, think of how it might be used as an attributive adjective (The en route barbarian checked his iron-age technology, maybe?), though it makes sense (I am en route) as a predicate. It’s probably worth taking a look a this definition from Merriam-Webster’s website, which provides a couple of useful definitions, as well as noting that en route, in terms of popularity, is in the top ten percent of words.
So it’s worth teaching to our students, at the very least, by the time they graduate from high school.
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