stündlich
hourly
At regular intervals of one hour; recurring every hour.
Die Fähre zur Insel verkehrt im Sommer stündlich.
The ferry to the island runs hourly in summer.

hourly
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hourly
At regular intervals of one hour; recurring every hour.
Die Fähre zur Insel verkehrt im Sommer stündlich.
The ferry to the island runs hourly in summer.

The word 'stündlich' (hourly) is derived from the noun 'die Stunde' (the hour) with the ending '-lich'. This pattern appears in many time expressions, e.g. 'täglich' (daily, from Tag), 'wöchentlich' (weekly, from Woche), or 'jährlich' (yearly/annually, from Jahr).
Wir haben eine wöchentliche Teambesprechung.
We have a weekly team meeting.
'Stündlich' (hourly) can be used as an adverb to indicate frequency: how often? It can also stand before a noun as an adjective and is then declined as usual.
Die Nachrichten werden stündlich aktualisiert.
The news is updated hourly.
When 'stündlich' (hourly) describes frequency as an adverb, it means 'jede Stunde' (every hour). When it stands as an adjective before nouns like 'Lohn' (wage) or 'Satz' (rate), it means 'pro Stunde' (per hour).
Der Bus zum Flughafen fährt stündlich.
The bus to the airport runs hourly.
for hours
'stundenlang' and 'stündlich' look similar and both have to do with hours. But they mean different things. 'stundenlang' describes a duration of several hours. 'stündlich' describes something happening every hour or at intervals of one hour. It is easy to confuse them because both come from 'Stunde' (hour). Memory aid: 'stundenlang' asks about length, while 'stündlich' asks about the interval or repetition.

Bei der Arbeit prüft das Team stündlich die neuen Nachrichten.
At work, the team checks the new messages hourly.
Zu Hause hat Tom stundenlang für die Prüfung gelernt.
At home, Tom studied for the exam for hours.