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to match (rhythm, speed, etc.)
to join together; to unite; to combine; to add up
to face; to be opposite (someone)
to compare; to check with
to cause to meet (e.g. an unpleasant fate)
to place together; to connect; to overlap
to mix; to combine
to put blade to blade; to fight
「合す」 has another reading with different meanings.
指揮者のリズムに合すように演奏を調整した。
The performance was adjusted to match the conductor's rhythm.
両手を合すと静かに目を閉じて祈り始めた。
Pressing both hands together, I quietly closed my eyes and began to pray.
相手の歩調に合すのは意外と難しいものだ。
Matching someone else's pace is surprisingly difficult.