Calling variable defined inside one function from another function

def anotherFunction(word):
    for letter in word:              
        print("_", end=" ")

def oneFunction(lists):
    category = random.choice(list(lists.keys()))
    word = random.choice(lists[category])
    return anotherFunction(word)

The simplest option is to use a global variable. Then create a function that gets the current word.

current_word = ''
def oneFunction(lists):
    global current_word
    word=random.choice(lists[category])
    current_word = word

def anotherFunction():
    for letter in get_word():              
          print("_",end=" ")

 def get_word():
      return current_word

The advantage of this is that maybe your functions are in different modules and need to access the variable.

Everything in python is considered as object so functions are also objects. So you can use this method as well.

def fun1():
    fun1.var = 100
    print(fun1.var)

def fun2():
    print(fun1.var)

fun1()
fun2()

print(fun1.var)

One approach would be to make oneFunction return the word so that you can use oneFunction instead of word in anotherFunction :

def oneFunction(lists):
    category = random.choice(list(lists.keys()))
    return random.choice(lists[category])

    
def anotherFunction():
    for letter in oneFunction(lists):              
        print("_", end=" ")

Another approach is making anotherFunction accept word as a parameter which you can pass from the result of calling oneFunction:

def anotherFunction(words):
    for letter in words:              
        print("_", end=" ")
anotherFunction(oneFunction(lists))

And finally, you could define both of your functions in a class, and make word a member:

class Spam:
    def oneFunction(self, lists):
        category=random.choice(list(lists.keys()))
        self.word=random.choice(lists[category])

    def anotherFunction(self):
        for letter in self.word:              
            print("_", end=" ")

Once you make a class, you have to instantiate an instance and access the member functions:

s = Spam()
s.oneFunction(lists)
s.anotherFunction()