It's there, but you need to know how to look for it.
First, since Google is displaying the adjectival definitions, we need to scroll down to the adjective definition in Merriam-Webster (the fourth of 4 definitions). There we find:
: being cramped
Some might say that circular definition is not very descriptive, but we can look at another part of the M-W entry, where we find:
: confine, restrain
When we put those two together, the resulting phrase being confined or restrained seems pretty much synonymous with uncomfortably small or restricted. After all, Google displays this definition for confined:
confined (adjective) (of a space) restricted in area or volume; cramped.