block vs block off

block is a noun but block off is not a noun.

Word	Noun	Adjective	Verb	Adverb
block	Yes	No	Yes	No
block off	No	No	Yes	No

As verbs, block and block off are synonyms defined as:

Other synonyms of block include bar, barricade, block up, blockade, stop.

As verbs, block off is a hyponym of block; that is, block off is a word with a more specific, narrower meaning than block:

Other hyponyms of block include close off, shut off, close.

As verbs, block off is a hyponym of block; that is, block off is a word with a more specific, narrower meaning than block:

block (noun)	block off (noun)
the act of obstructing or deflecting someone's movements
a solid piece of something (usually having flat rectangular sides)
an obstruction in a pipe or tube
a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope
a metal casting containing the cylinders and cooling ducts of an engine
a platform from which an auctioneer sells
housing in a large building that is divided into separate units
an inability to remember or think of something you normally can do; often caused by emotional tension
a number or quantity of related things dealt with as a unit
a rectangular area in a city surrounded by streets and usually containing several buildings
(computer science) a sector or group of sectors that function as the smallest data unit permitted
a three-dimensional shape with six square or rectangular sides

block (verb)	block off (verb)
shape into a block or blocks	obstruct access to
shape by using a block	render unsuitable for passage
prohibit the conversion or use of (assets)	block off the passage through
be unable to remember
interfere with or prevent the reception of signals
impede the movement of (an opponent or a ball)
render unsuitable for passage
obstruct
stamp or emboss a title or design on a book with a block
support, secure, or raise with a block
block passage through
shut out from view or get in the way so as to hide from sight
interrupt the normal function of by means of anesthesia
hinder or prevent the progress or accomplishment of
stop from happening or developing
run on a block system