masslos
excessive
To an extreme or exaggerated extent; without any moderation or limit.
Sein massloser Konsum führte schnell zu hohen Schulden.
His excessive consumption quickly led to high debts.

excessive
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excessive
To an extreme or exaggerated extent; without any moderation or limit.
Sein massloser Konsum führte schnell zu hohen Schulden.
His excessive consumption quickly led to high debts.

The word is made up of 'Maß' (measure) and the ending '-los' (-less). The ending '-los' means 'without', so 'maßlos' literally means 'without measure'.
Ihre Erwartungen an das Projekt waren maßlos übertrieben.
Her expectations for the project were excessively exaggerated.
'Maßlos' is very often used as an adverb to intensify another adjective or a verb. It then means 'extremely' or 'very strongly'.
Nach der Absage war er maßlos enttäuscht.
After the cancellation, he was extremely disappointed.
In the meaning of 'übertrieben' (exaggerated), 'maßlos' is often combined with negative behaviors or qualities. Typical examples are 'maßloser Ehrgeiz' (excessive ambition), 'maßlose Gier' (excessive greed), or 'maßlose Verschwendung' (excessive wastefulness).
Seine maßlose Gier nach Macht hat ihn isoliert.
His excessive greed for power isolated him.
When it comes to feelings, 'maßlos' describes their extreme intensity. Common combinations are 'maßlose Wut' (boundless anger), 'maßlose Trauer' (boundless grief), or 'maßlose Freude' (boundless joy).
Als sie die Nachricht hörte, empfand sie eine maßlose Wut.
When she heard the news, she felt boundless anger.
extreme
'extrem' and 'masslos' both describe a very high degree. However, 'extrem' can be used more broadly: you can talk about 'extreme Hitze' (extreme heat), 'extreme Preise' (extreme prices), or 'extreme Bedingungen' (extreme conditions). 'masslos' sounds more like exaggeration and a lack of limits. It fits especially when someone wants too much, reacts too strongly, or a feeling is very intense. 'extrem' can be more neutral; 'masslos' often sounds more critical.

Der Kunde war masslos wütend, obwohl der Fehler schnell behoben wurde.
The customer was boundlessly angry, even though the mistake was fixed quickly.
Nach dem Sturm waren die Straßen extrem glatt.
After the storm, the roads were extremely slippery.