Regex replace is taking time for millions of documents, how to make it faster?

I have documents like:

documents = [
    "I work on c programing.",
    "I work on c coding.",
]

I have synonym file such as:

synonyms = {
    "c programing": "c programing",
    "c coding": "c programing"
}

I want to replace all synonyms for which I wrote this code:

# added code to pre-compile all regex to save compilation time. credits alec_djinn

compiled_dict = {}
for value in synonyms:
    compiled_dict[value] = re.compile(r'\b' + re.escape(value) + r'\b')

for doc in documents:
    document = doc
    for value in compiled_dict:
        lowercase = compiled_dict[value]
        document = lowercase.sub(synonyms[value], document)
    print(document)

Output:

I work on c programing.
I work on c programing.

But since the number of documents is a few million and the number of synonym terms are in 10s of thousands, the expected time for this code to finish is 10 days approx.

Is there a faster way to do this?

PS: with the output I want to train word2vec model.

Any help is greatly appreciated. I was thinking of writing some cpython code and putting it in parallel threads.