This is the 5464th most frequent Polish word.
tamtej
"Tamtej" means "that" (referring to a specific feminine noun in the dative or genitive case).
The word 'tamtej' is used here as a feminine genitive singular adjective modifying the noun 'zimy' (winter), referring to a specific past season, indicating its relation to the speaker in the past.
Tamtej zimy było bardzo mroźno.
That winter was very cold.
'Tamtej' here is a feminine genitive singular adjective referring to the noun 'książki' (book), signifying a specific book previously mentioned or understood from context.
Nie mogę znaleźć tamtej książki na półce.
I can't find that book on the shelf.
In this sentence, 'tamtej' is a feminine genitive singular adjective modifying the noun 'osoby' (person), used to indicate a specific person within the context provided.