This is the 6022nd most frequent Polish word.
ac
The word "ać" is not a standalone word in Polish but appears as an infinitive verb ending, such as in "robić" (to do).
In this sentence, 'ac' is used as a conjunction equivalent to 'but', indicating a contrast between two clauses.
Musiałem skończyć pracę wcześniej, ac nie mogłem.
I had to finish work earlier, but I couldn't.
Here, 'ac' is again employed as a conjunction contrasting the conditions described in the two clauses.
Słońce świeciło jasno, ac wiał chłodny wiatr.
The sun was shining brightly, but a cool wind was blowing.
The word 'ac' is used here to express an opposition or difficulty in accepting juxtaposed statements.