You have to figure this is something you stick in your mouth. But what? If you don’t know, there are a few possible guesses.
You’ll most likely proceed first on the basis of sub + gum. Is it something you put under your gums? How would you do that – would it be like that nasty Skoal tobacco that you (or someone you’d rather not stand too close to) stick between cheek and gum, provoking excessive expectoration? Or is it something that simply seems to support your gums? Perhaps something toothsome? Or is it like a gum but less so? Or a substrate for a gum? Or is it a gangster chew (as in submachine gum)?
But, then, what if it’s not sub + gum? Perhaps it’s like gumbo. Or perhaps it’s like sorghum. Maybe it’s a kind of backwards humbug. Where is this word from, anyway? It could be from Latin, if it’s sub + gum, but perhaps it’s from Hindi – it has that sort of sound. Or is it from an African language? The /bg/ could be a coarticulation… This word, so simple-looking, really does seem to have a whole mix of possibles in its soft, quick two-syllable double bump.
The clue that will help solve it for you is that it is typically followed by one of the following pairs of words: chow mein, lo mein, or chop suey.
Yes, if you’ve seen this word, it’s probably been on a Chinese restaurant menu, in particular an Americanized one. It comes from Cantonese sap gam “numerous and varied” or “mixture” – one might say “bits ’n’ bites”, “allsorts”, “this ’n’ that”… The dish it names has a mixture of various vegetables. There’s often also some kind of formerly animate stuff (that’s the word that comes before subgum: chicken subgum, pork subgum, seafood subgum, etc.). And you may expect some noodles if, for instance, it’s chicken subgum chow mein.
But, now, just tell me the truth: doesn’t it seem a bit like it’s somehow substandard or insufficiently something or other? When I see sub somewhere, that’s the default expectation in the absence of some root that makes it something else (substance, submit, submarine, etc.). It’s either that or it’s under something. And the gum gives it that soft feeling. You almost feel like it should be some suspicious glutinous mass. And instead you get crispy mixed vegetables (and nary a slice of gumbo in sight). Ah, dumb-dumb, it’s yum-yum! So num-num!