Meaning of ざがしら in Japanese

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Definition of ざがしら

ざがしら(zagashira) 【座頭】

ひざがしら(hizagashira) 【膝頭 ·膝がしら】

ざがしらける(zagashirakeru) 【座が白ける ·座がしらける】

(exp, v1) to put a damper on proceedings (e.g. at a meeting or party, etc.)
ちょっと座が白けている。
There is a slight chill on the party.