kubuto

One root, and no suffix hiding in it. Kubuto is kubut- plus -o, and that is all. Esperanto has no -ut- suffix - there is no such thing - so there is nothing to strip and nothing to guess. The word looks analysable because Esperanto trains you to look for seams; this is a page where the honest answer is that the seam does not exist. The same goes for genuo, the knee, and stomako.

The joints, in order. Ŝultro is the shoulder, kubuto the elbow, pojno the wrist, and the whole limb is the brako. Downstairs the pattern repeats: kokso the hip, genuo the knee, maleolo the ankle. Esperanto borrows each of these whole from Latin rather than compounding them, which is unusual for the language and simply reflects that anatomy came into it from medical vocabulary.

Idiom. Kubuti is to elbow your way through - the verb is made from the noun with nothing added but the -i, the way Esperanto lets any root become any part of speech. Kubutumi is the affectionate version, to nudge. And havi liberajn kubutojn, to have your elbows free, means to have room to act, which is a picture worth borrowing back into English.