noun
sei whale
A species of baleen whale (Balaenoptera borealis).
イワシクジラはナガスクジラに似ているが、やや小さい。
The sei whale resembles the fin whale but is slightly smaller.
Compound of 鰯 (いわし, 'sardine') + 鯨 (くじら, 'whale'), likely referring to its diet or the sardine-like appearance of its baleen. The exact origin is uncertain.