This is the 3232nd most frequent Catalan word.
sencera
Whole; entire.
Here, "sencera" is an adjective that modifies "poma" (apple) to indicate that it was whole and not divided.
Vaig menjar una poma sencera.
I ate an entire apple.
In this example, "sencera" is describing "setmana" (week) to emphasize that it's the duration of a full week.
Aquest projecte requerirà una setmana sencera.
This project will require a whole week.
Here, "sencera" is used figuratively to modify "culpa" (responsibility) to convey totality or completeness in an abstract sense.