zweit-
second
Indicates position two in an order or ranking. It is always used in declined form (zweiter, zweite, zweites).
Er kam als Zweiter ins Ziel.
He crossed the finish line in second place.

second
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second
Indicates position two in an order or ranking. It is always used in declined form (zweiter, zweite, zweites).
Er kam als Zweiter ins Ziel.
He crossed the finish line in second place.

The word 'zweit-' (second) is often used as a prefix in compound words. It then means 'standing in second place' or 'secondary.'
Hamburg ist die zweitgrößte Stadt Deutschlands.
Hamburg is Germany's second-largest city.
The form 'zweit' does not exist on its own. As an ordinal number, it is always adapted to the gender of the noun and declined: 'der zweite Platz' (second place), 'die zweite Chance' (second chance), 'das zweite Mal' (the second time).
Ich lese gerade das zweite Kapitel.
I'm currently reading the second chapter.
The expression 'zu zweit' means 'as a pair' or 'as a group of two people.' This construction with 'zu' can also be formed with other numbers to indicate the size of a group.
Lass uns den Film zu zweit ansehen.
Let's watch the film as a pair.
The combination 'jeder zweite' (or 'jede zweite', 'jedes zweite') is used to express a frequency of 50% or an alternating order. The adjective 'zweite' is declined in this construction.
Jeder zweite Deutsche besitzt ein Fahrrad.
Every other German owns a bicycle.
two
'zwei' and 'zweit-' look similar, but they have different functions. 'zwei' names a quantity: there are exactly 2 people or things. 'zweit-' describes position number 2 in a sequence, for example 'der zweite Tag' (the second day). In the form 'zu zweit', it means that two people do something together. In 'jeder zweite' (every other), it is about a regular selection. Learners confuse the words because both have to do with 2. Remember: quantity = 'zwei', order = 'zweite', together with one other person = 'zu zweit'.

Der zweite Termin ist erst morgen Nachmittag.
The second appointment is not until tomorrow afternoon.
Im Zug sitzen zwei Kinder am Fenster.
Two children are sitting by the window on the train.