kristalo

A false seam, and a well-laid one. Kristalo looks like Krist- plus a suffix -al-. Both halves of that reading are wrong, and the trap is fair rather than silly, because the pattern really does exist elsewhere: kristano genuinely contains the root Krist-, built with -an- for an adherent. But kristal- is a single Greek root with no religious content whatever, and Esperanto has no suffix -al- at all. Ido adopted one; Esperanto never did. The same non-suffix turns up on sociala elsewhere in this chapter, so it is worth learning once and applying twice.

The Greek is worth keeping, because it explains a sentence that otherwise reads as a mere simile. Krystallos meant ice, and only later the mineral, since the ancients thought rock crystal was water frozen past thawing. So when Esperanto puts kristalo and glacio in the same breath - klara kiel kristalo - it is not reaching for a comparison. It is repeating, without meaning to, an idea two and a half thousand years old.

The derivations are regular: kristala (crystalline, and figuratively crystal-clear), kristaliĝi (to crystallise, of the thing itself), kristaligi (to crystallise something else), kristalvitro for crystal glassware, and neĝkristalo for a snowflake.