This is the 12943rd most frequent German word.
zittrain
The German word "Zittrain" does not exist; it may be a misunderstanding or a misspelling.
Here, 'zitternd' is the gerund form of the verb 'zittern,' related to trembling or shivering.
Ich werde nicht zitternd auf den nächsten Zug warten.
I will not wait for the next train shivering.
'Zitternd' describes the condition of the hand in the state of trembling due to excitement.
Seine Hand war vor Aufregung zitternd.
His hand was trembling with excitement.
'Zitternd' is used as an adjective to describe the leaf trembling as it falls.