der Käpt'n
cap'n
A colloquial and shortened form of captain, especially for the leader of a ship.
Der Käpt'n gab den Befehl, die Segel zu setzen.
The cap'n gave the order to set the sails.

cap'n
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cap'n
A colloquial and shortened form of captain, especially for the leader of a ship.
Der Käpt'n gab den Befehl, die Segel zu setzen.
The cap'n gave the order to set the sails.

'Käpt'n' is the colloquial short form of 'Kapitän' (captain). The apostrophe (') shows that letters have been left out. This form is used mainly in spoken language or in informal texts.
„Aye, aye, Käpt'n!“, rief der Matrose.
'Aye, aye, cap'n!' shouted the sailor.
The word is used almost exclusively in the context of seafaring. It often creates an atmosphere of adventure, pirates, or old sailing ships, as you might know from films and books.
Der alte Käpt'n erzählte Geschichten von seinen Reisen auf hoher See.
The old cap'n told stories of his voyages on the high seas.
'Käpt'n' is often used as a direct form of address for the leader of a ship, similar to saying 'Captain' in English.
Käpt'n, wir haben Land in Sicht!
Cap'n, we have land in sight!
captain
'der Kapitän' and 'der Käpt'n' often refer to the same person in the context of a ship: the leader on board. The difference is mainly in style. 'Kapitän' is the normal and neutral form and fits in almost all situations. 'Käpt'n' is a short, colloquial form and sounds more casual, often also somewhat maritime or storytelling-like. The words can be confused because they are very close in meaning. In official or factual texts, 'Kapitän' is more natural; in casual conversations or stories, 'Käpt'n' can fit well.

Der Käpt'n rief den Gästen zu, dass die Fahrt gleich beginnt.
The cap'n called out to the guests that the trip was about to begin.
Der Kapitän kontrollierte vor der Reise die Wetterberichte.
The captain checked the weather reports before the trip.