noun
first autumn maple leaves to turn red
A seasonal word (kigo) used in haiku and traditional poetry to refer to the earliest maple leaves that change color in autumn. In everyday language, it may be used to describe the first signs of autumn foliage.
庭の初紅葉が美しい。
The first red maple leaves in the garden are beautiful.
初紅葉を見に山へ行った。
I went to the mountains to see the first autumn maple leaves.
紅葉 refers to autumn leaves in general or the process of leaves changing color, while 初紅葉 specifically means the very first maple leaves to turn red in the season.
もみじ is the common word for maple tree or its leaves, often used for autumn foliage. 初紅葉 adds the nuance of 'first' and is more poetic.
Compound of 初 (hatsu, 'first') and 紅葉 (momiji, 'maple leaves turning red'). The reading はつもみじ is standard; the longer readings はつもみじば and はつもみちば are obsolete.