noun
autumn horse mackerel
Refers specifically to horse mackerel (aji) caught in autumn, when it is considered especially fatty and flavorful. A seasonal food term; the word itself is not common in everyday conversation but appears in culinary or fishing contexts.
秋鯵は脂がのっていて刺身に最適だ。
Autumn horse mackerel is fatty and perfect for sashimi.
市場で立派な秋鯵を見つけた。
I found some fine autumn horse mackerel at the market.
鯵 is the general term for horse mackerel regardless of season; 秋鯵 specifies the autumn catch, prized for its flavor.
Compound of 秋 (aki, 'autumn') and 鯵 (aji, 'horse mackerel'). The exact historical origin is uncertain, but it is a straightforward seasonal food name.