instrumental
Refers to music that is played only with instruments and without singing.
Die B-Seite der Single war eine instrumentale Version des Liedes.
The B-side of the single was an instrumental version of the song.

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Refers to music that is played only with instruments and without singing.
Die B-Seite der Single war eine instrumentale Version des Liedes.
The B-side of the single was an instrumental version of the song.

You can easily recognize the meaning of 'instrumental' from context. If it is about music, the first meaning is meant. If it is about the success of a project, the second is meant. In the context of grammar, the third is meant.
Ich höre beim Arbeiten gerne instrumentale Musik.
I like listening to instrumental music while working.
In the figurative meaning, 'instrumental' is often used in the fixed expression 'instrumental für etwas sein' (to be instrumental in/for something). The noun after 'für' is in the accusative.
Ihre Unterstützung war instrumental für den Erfolg des Teams.
Her support was instrumental in the team's success.
In a musical context, 'instrumental' often appears with words like 'Version' (version), 'Stück' (piece), 'Musik' (music), or 'Begleitung' (accompaniment).
Der Song wurde auch als rein instrumentales Stück veröffentlicht.
The song was also released as a purely instrumental piece.
The grammatical meaning of 'instrumental' is a technical term from language studies (linguistics). This meaning does not occur in normal everyday usage.
In der Vorlesung haben wir die Funktion des Instrumentals in slawischen Sprachen besprochen.
In the lecture, we discussed the function of the instrumental in Slavic languages.
essential / significantly
'wesentlich' and 'instrumental' can both express that something is very important for an outcome. 'wesentlich' says generally that something is essential, decisive, or fundamental. 'instrumental' is used more specifically when a person, measure, or thing contributes strongly to something succeeding. It sounds more technical or elevated and often appears in phrases like 'instrumental für den Erfolg' (instrumental to the success). In everyday language, 'wesentlich' is usually more natural. 'instrumental' fits when you want to emphasize that something was an important means or a decisive contribution to an outcome.

Die Unterstützung der Nachbarn war instrumental für den schnellen Umzug.
The neighbors' support was instrumental in the quick move.
Nach der Arbeit ist mir eine ruhige Pause wesentlich.
After work, a quiet break is essential to me.