Refers to idle talk, pointless matters, or trivial things not worth serious attention. Often used in the phrase よしなし事を言う (to talk nonsense).
He is always talking nonsense.
We wasted time on trivial matters in the meeting.
つまらないこと is a more common and general expression for 'trivial thing', while よしなし事 has a slightly literary or old-fashioned flavor.
Standard kanji-kana mixed spelling; the most common written form.
Literary kanji spelling using 由; rarely used in modern writing.
Variant literary kanji spelling; rarely used in modern writing.
From よしなし (meaningless, trivial) + 事 (thing). The exact historical derivation of よしなし is uncertain, but it is a classical Japanese adjective meaning 'without reason' or 'pointless'.