This is the 59th most frequent Hungarian word.
kellett
"Kellet" means "was necessary" or "had to".
The word 'kellett' is used in the past tense, indicating an obligation or necessity that the subject had in the past.
El kellett mennem az iskolába tegnap.
I had to go to school yesterday.
In this sentence, 'kellett' is part of the conditional past, expressing something that ought not have been done.
Akkor nem kellett volna hazudnod neki.
You shouldn't have lied to him then.
Here, 'kellett' is used to express a missed obligation or recommendation in the past.