In English:
* "la" is not a stand-alone word. It is used as part of a word, like in "la-di-da" or "la-la-land."
* It can be used as a filler word in casual conversation, like "la-la-la."
In other languages:
* "la" can be a definite article like "the" in Spanish, Italian, French, Portuguese, and Romanian.
* "la" can be a musical note.
Therefore, it is impossible to determine the "base word" of "la" because it doesn't have a stand-alone meaning in English.
Could you please clarify what you mean by "base word" in this context? Perhaps you are referring to a specific language other than English?