noun
bowl and shank of a Japanese pipe
Refers specifically to the metal head of a kiseru (Japanese pipe), consisting of the bowl and the shank.
祖父の形見の煙管の雁首は銀でできている。
The bowl and shank of my grandfather's keepsake kiseru are made of silver.
あいつら、また雁首そろえて何か企んでるぞ。
Those guys are lining up together again, plotting something.
酔っ払って雁首を振りながら歩いている。
He's walking along, drunk, swaying his head.
Literally 'goose neck', from the resemblance of the curved pipe head to a goose's neck. The colloquial sense for a person's neck is a metaphorical extension.