He had to swallow his anger during the negotiation to avoid escalating the conflict.

swallow 在这里是动词，本意是"吞咽"，引申为"忍受、压抑"情绪或话语。 his 是代词 he 的所有格形式，表示"他的"。 anger 是名词，意思是"愤怒、怒气"。 swallow one's anger 是一个固定短语，字面意思是"咽下愤怒"，实际表示"强压怒火、忍气吞声"的意思。