This is the 2019th most frequent German word.
langem
"Langem" is the dative singular form of "lang" (long) used in contexts like "seit langem," meaning "for a long time."
'langem' is used as a dative form to indicate the duration of waiting.
Nach langem Warten endlich gute Nachrichten.
After a long wait, finally good news.
'langem' is used as a dative form to specify the length of the search period.
Er fand nach langem Suchen die Lösung.
He found the solution after a long search.
'langem' here denotes a qualitative length in time, with 'Vergangenem' in dative indicating the past.