ŝaŭmo

One root, ŝaŭm-, and nothing hiding in it. The -aŭ- is a single vowel, a diphthong, so the word has two syllables and not three: ŝaŭ-mo. Learners coming from Spanish or Italian reliably want to make three of it. The Sound Lab has the diphthong if you want to hear it.

Ŝaŭmo covers the whole territory English splits between foam, froth, lather and head. Sea foam on the sand, the head on a beer, the lather from soap, the white on a horse that has been ridden too hard, and the modern plastic material: plastŝaŭmo or ŝaŭmplasto is what a cushion or a packing insert is made of. English needs four or five words there and Esperanto needs one, which for once is the direction that favours the learner.

The verb is where the metaphor lives. Ŝaŭmi is to foam, and it is intransitive: la maro ŝaŭmas, the sea is foaming. Figuratively it does the same job as in English, ŝaŭmi pro kolero, to foam with rage. Ŝaŭmigi is to cause something to foam, which is what you do to egg whites, and the resulting stiff foam is a ŝaŭmaĵo. Senŝaŭmigi is to skim the scum off a stock, and it is an ordinary word in a recipe.

Do not reach for it for bubbles. A single bubble is a veziko and a fizzy drink is gasa or ŝaŭmanta depending on whether you mean the carbonation or the visible froth; sparkling wine is ŝaŭmvino, which is exactly the German Schaumwein and one of a fair number of places where Esperanto's compounding instincts came out of German rather than French.