expression, suru verb (irregular)
share a cup of sake; drink sake together in commemoration
Used for a ceremonial or commemorative sharing of sake, often to mark an agreement, reconciliation, or special occasion. The phrase implies a symbolic act rather than casual drinking.
和解のしるしに、二人は杯をした。
As a sign of reconciliation, the two shared a cup of sake.
杯を交わす also means to exchange sake cups, often in a more formal or ritualized context such as a wedding or pledge. 杯をする is slightly broader and can refer to the act of sharing a cup in commemoration.
The expression combines 杯 (sakazuki, 'sake cup') with する ('to do'), literally 'to do the sake cup'. The exact historical derivation is uncertain, but it is a set phrase for the act of sharing sake ceremonially.