na-adjective, noun
Describes matters, details, or differences that are so small or unimportant that they are not worth serious attention. Often used in formal or critical contexts to dismiss something as insignificant.
そんな瑣末な問題に時間をかけるべきではない。
We shouldn't spend time on such a trivial issue.
両者の違いは瑣末な点に過ぎない。
The difference between the two is nothing more than a minor point.
些細 (ささい) is more common in everyday speech for 'trivial, minor'. 瑣末 (さまつ) is slightly more formal and often used in written or critical contexts.
つまらない means 'boring, dull' or 'trivial' in a more casual, subjective sense. 瑣末 is objective and focuses on insignificance rather than lack of interest.
The word is a combination of 瑣 (さ, 'small, trivial') and 末 (まつ, 'end, tip, trivial'). The kanji 瑣 is relatively rare and carries the meaning of 'small' or 'petty'. The alternative spelling 些末 uses 些 (さ, 'a little, small') which is more common. The exact historical derivation is uncertain, but the word has been used in written Japanese since at least the early modern period.