sit-in
1936, in reference to session musicians; 1937, in reference to union action; 1941, in reference to student protests. From the verbal phrase; see sit, v. + in, adv.. To sit in is attested from 1868 in the sense "attend, be present;" from 1919 specifically as "attend as an observer."
〔李〕n. 静坐示威 ←-in [MnE] 表示“有组织的抗议或示威”、“公开的集体活动”