This is the 5009th most frequent Japanese word.
美味かっ
"美味かっ" is not a complete word; it appears to be part of "美味しかった," meaning "was delicious."
美味かった is the past form of 美味しい (delicious), describing the quality of the cooking.
彼の料理はとても美味かったです。
His cooking was very delicious.
美味かった is used in the context of past enjoyment of sushi during travel.
旅行中に食べた寿司が美味かった。
The sushi I ate during the trip was delicious.
美味かった is expressing a past impression of the quality of the cake.