This is the 45th most frequent Hungarian word.
amit
"That which" or "what."
'Amit' functions here as a relative pronoun introducing the description of 'the thing' (a dolog), specifying what was said.
Emlékszel arra a dologra, amit mondtam tegnap?
Do you remember the thing that I said yesterday?
In this example, 'amit' serves as a relative clause connector to elaborate on 'all' (mindaz), detailing the actions that were helpful.
Mindaz, amit tettél, nagy segítség volt.
All that you did was a great help.
Here, 'amit' is used as a relative pronoun referring to 'book' (könyv), linking the relative clause to the main clause and describing the object of my liking to read.