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1. To obstruct. This cold is blocking up my nose and I can hardly breathe. One of the kids flushed some action figures, which are now blocking up the pipes.
2. To make one constipated. In this usage, a noun or pronoun is used between "block" and "up." That type of food always blocks me up—I was constipated for days the last time I ate it.
block someone up*
to constipate someone. That food always blocks me up. He blocked himself up by eating something he shouldn't. That vile stuff would block up anybody!
block something up
to obstruct something; to stop the flow within a channel. The heaps of debris blocked the channel up. The leaves blocked up the drain.
1. To obstruct something, as a passageway: The stalled truck blocked up the road. The old leaves are blocking up the drainage pipes.
2. To cause something to become obstructed: The soldiers blocked up the tunnel with barbed wire. A bad head cold has blocked my sinus passages up.
3. To become obstructed: My arteries had blocked up, so my doctor put me on a special diet.