ŝelo

One Esperanto word does the work of half a dozen English ones. Ŝelo is the outer layer of anything that protects what is inside: the bark of a tree, the peel of an apple, the rind of a cheese, the shell of an egg or a crab, the hull of a ship (ŝipŝelo), even the crust of the earth (terŝelo). Computing borrowed it too, exactly as English did: the ŝelo is the program wrapped round the kernel.

The useful derivations follow the shape of the thing. Senŝeligi is to peel or shell something (take its ŝelo away); a senŝeligilo is a peeler; elŝeligi is to get something out of its shell, and figuratively to bring a point out clearly. Nuksoŝele means "in a nutshell".

The minimal pair, and it is a nasty one. Ĉelo (rank 1911) is a cell: a biological cell, a prison cell, a cell of a honeycomb. Ŝelo is a shell. One hat apart on the page, and they are opposites in a small way that matters - a ĉelo is the compartment, a ŝelo is the wrapping round it. The saving grace is that they sound nothing alike: ĉ is the "ch" of church, ŝ is the "sh" of ship. Read your Esperanto out loud and the pair separates itself. Read it silently in the x-system, where they are cxelo and sxelo, and you will mix them up for a month.