Print one word from a list within a dictionary (python)

I want my program to print only one random word from the list within my dictionary, but I can't seem to get the right syntax to do so. I attempted using popitem() to get a random value from the list, but it doesn't seem to be working. Here is my code:

import random

thesaurus = {
              "happy":["glad",  "blissful", "ecstatic", "at ease"],
              "sad"  :["bleak", "blue", "depressed"]
            }

# input
phrase = input("Enter a phrase: ")

# turn input into list
part1 = phrase.split()
part2 = list(part1)

newlist = [] 
for x in part2:
    s = thesaurus.get(x, x)
    newlist.append(s)

print (newlist)

For example, if the input is

i am happy

The expected output would be

i am glad

or any random word from the list within the dictionary.

But, right now my output looks like this:

['i', 'am', ['glad', 'blissful', 'ecstatic', 'at ease']]

I know there is another thread involved with this, but it doesn't seem to address this specific issue.

Any help would be appreciated!