der Akkord
chord
In music, the simultaneous sounding of at least three different notes that are harmonically related.
Der Gitarrenlehrer zeigte ihr, wie man einen C-Dur-Akkord greift.
The guitar teacher showed her how to finger a C major chord.

chord / piecework
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chord
In music, the simultaneous sounding of at least three different notes that are harmonically related.
Der Gitarrenlehrer zeigte ihr, wie man einen C-Dur-Akkord greift.
The guitar teacher showed her how to finger a C major chord.

'Akkord' has two main meanings, which you can recognize from the context and the grammar. In music, people speak of 'einem Akkord' (a chord), for example on an instrument. In a work context, the fixed expression 'im Akkord' is almost always used to describe working quickly.
Er übt einen neuen Akkord auf der Gitarre.
He is practicing a new chord on the guitar.
In a musical context, 'Akkord' is often combined with the verbs 'spielen' (to play), 'greifen' (to finger, with string instruments), or 'drücken' (to press, with keyboard instruments).
Kannst du diesen Akkord auf dem Klavier spielen?
Can you play this chord on the piano?
The meaning 'to work quickly' is used almost exclusively in the fixed expression 'im Akkord' or 'im Akkord arbeiten' (to work at piecework pace). The preposition 'im' is a fixed part of the expression here.
Vor Weihnachten arbeiten die Zusteller oft im Akkord.
Before Christmas, delivery drivers often work at piecework pace.
melody
'Melodie' and 'Akkord' both belong to music and describe notes. The difference is important: a melody is a sequence of notes one after another, which you can often sing along to or recognize. A chord consists of several notes that sound at the same time and accompany or support the sound. Learners may confuse the words because both occur when playing a song. In practical terms: you often sing the melody, while you play the chord along with it, for example on the guitar or piano.

Tom übt auf der Gitarre einen neuen Akkord für das Lied.
Tom is practicing a new chord for the song on the guitar.
Nach dem Konzert hatte Lisa die Melodie noch den ganzen Abend im Kopf.
After the concert, Lisa still had the melody in her head all evening.