1.
If someone blocks out a thought, they try not to think about it.
She accuses me of having blocked out the past...
I had to block the thought out of my mind.
PHRASAL VERB: V P n (not pron), V n P of n
2.
Something that blocks out light prevents it from reaching a place.
Thick chipboard across the window frames blocked out the daylight...
Those clouds would have cast shadows that would have blocked some sunlight out.
PHRASAL VERB: V P n (not pron), V n P