To match rhythm, tempo, speed, etc.; to synchronize with something or someone.
演奏者たちはテンポを合わせて曲を始めた。
The musicians started the piece after matching their tempo.
歩く速さを合わせて、彼女はゆっくりと横を歩いた。
She walked alongside him, matching his pace slowly.
時計の時間をサーバーの時刻に合わせてください。
Please set your watch to the server time.
To join, unite, combine, or add up things; to bring parts or elements together into one.
材料を合わせて新しい合金を作った。
They combined materials to make a new alloy.
売上を合わせると、今月は目標を超えた。
Adding up the sales, we exceeded the target this month.
みんなの力を合わせれば、問題は解決できる。
If everyone combines their efforts, the problem can be solved.
To face someone; to be opposite someone; to meet someone face to face (often used in the set phrase 顔を合わせる).
彼とは職場で毎日顔を合わせる。
I see him face to face at work every day.
会議で初めて直接顔を合わせて話した。
We met and spoke face to face at the meeting for the first time.
長年会っていなかった父と、突然顔を合わせることになった。
I unexpectedly had to face my father, whom I hadn't seen for many years.
To compare or check against something; to verify by cross-checking records, data, or lists.
名簿を出席表と合わせて確認してください。
Please check the roster against the attendance sheet.
請求書の金額を領収書と合わせて照合した。
I compared the invoice amounts with the receipts.
翻訳の訳語を原文と合わせて調整する。
I adjust the translated terms by comparing them with the original text.
Literary/older usage meaning to cause someone to meet or encounter (often an unpleasant fate). In modern Japanese, 遭わせる is more common.
戦争は多くの人々を悲劇に合わせた（＝悲劇に遭わせた）。
War brought tragedy upon many people (i.e., caused them to encounter tragedy).
To place together, connect, or overlap things; to align positions or shapes so they match.
写真の端を合わせてアルバムに貼った。
I aligned the edges of the photos and pasted them into the album.
パズルのピースを合わせていくと絵が完成する。
If you fit the puzzle pieces together, the picture will be completed.
パネルをつなぎ合わせて大きな表示を作った。
We connected the panels to make a large display.
To mix or combine ingredients or components (e.g., seasonings, colors).
しょうゆとみりんを合わせてタレを作る。
Mix soy sauce and mirin to make the sauce.
絵の具を合わせて微妙な色を作った。
I mixed paints to create a subtle color.
二種類の素材を合わせた新しい布が販売された。
A new fabric combining two materials was sold.
To put blades or swords against each other; to fight or duel (often in expressions like 刃を合わせる).
剣道の試合で二人は刃を合わせた。
In the kendo match the two faced each other with swords.
古い映画で決闘シーンは、二人が刀を合わせる場面だった。
In the old movie, the duel scene showed the two bringing their blades together.