The correct spelling of the word is "nuclear" /njuː.kli.ər/. This word comes from the nucleus, which is the central part of an atom. It is pronounced with a stress on the second syllable, and the vowel sound in the first syllable is a "yu" sound, as in "new" or "cue". The spelling "nucler" is incorrect and may be a common misspelling due to the pronunciation of the word. It is important to use the correct spelling in communication to avoid confusion and misunderstandings.