There are at least ten German verbs that have unique meanings when connected with lassen ("to let"). Not so very long ago, they were literally connected with lassen in that they used to be written together as a single verb. However, in the last decades, the arbiter of German grammar, Duden, proclaimed that it is preferable grammatically to write the root verbs and lassen as separate words. Oddly enough, rather than subordinating the version with lassen to the main listing for the verb in question, Duden still has them listed in a dictionary single entry -- for two verbs. Thus if you search on Duden for the old spelling of fallenlassen, the first match will be fallen lassen.

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Here are some examples of verbs connected to lassen which in the past would have been written as a single verb, but are now usually separated by a space:

Und als sich der Mond schließlich zeigte,

And when the moon finally revealed itself,

glänzten die weißen Kieselsteine, die Hänsel hatte fallen lassen,

the white pebbles that Hansel had let fall gleamed

wie Silber.

like silver.

Captions 31-32, Märchen - Sagenhaft - Hänsel und Gretel

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Ich bin locker. Wenn ich will, kann ich mich total gehen lassen.

I am relaxed. If I want to I can totally let myself go.

Caption 26, Filmtrailer - Keinohrhasen

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Ansonsten gilt im Zoo weiterhin die Frühlingsdevise:

Apart from that, in the zoo the spring slogan still applies:

einfach mal hängen lassen!

at times simply just let it all hang out!

Caption 48, Rheinmain im Blick - Frühling im Zoo

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Diese Knochen macht dem Greifvogel kein Futterrivale streitig,

No rival will fight the bird of prey for these bones,

deshalb kann er sie ruhig liegen lassen.

so it can leave them well alone.

Captions 46-47, Die letzten Paradiese - Die Schönheit der Alpen 1

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Den Teig lassen wir jetzt fünfundvierzig Minuten ruhen.

We'll let the dough sit now for forty-five minutes.

Caption 33, Bundesländer und ihre Rezepte - Bayern

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Und somit hab ich dann alles, was mit Studium und Musik zu tun hatte, erst mal sein lassen.

And with that, I then let everything go that had to do with university studies and music.

Caption 44, Powerfrau - Lina bleibt auf dem Boden

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Sie haben meiner Tochter schöne Augen gemacht und sie dann sitzen lassen.

You made eyes at my daughter and then abandoned her.

Caption 20, Oskar - Gehen, wenn es am schönsten ist - Loslassen

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Man sollte ihn besser für alle Zeiten stehen lassen.

You'd be better off to leave it there for all time.

Caption 35, Piggeldy und Frederick - Regenbogen

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As an added note, there are many other verbs ending with lassen that are still written as one word. Most of them have adjectives or adverbs as prefixes. Go to this link at dict.cc and see many examples.

Further Learning
See if you can guess the meanings of bleiben lassen and fahren lassen and then check a German dictionary to see if you got them right. You can also look for more examples of the above verbs related to lassen on Yabla German.