If there’s a method for investigation then it’s a science.
there’s a number of decent synonyms for a science in that context.
but it can be defined by contrast:
“A science of”
can be contrasted with “philosophy of”.
A science could be thought of as “a philosophy of ” among others whereby the “science of” is of the commonly accepted norms but the “philosophy of” is more speculative and has the room to question itself more thoroughly.
in this, the theoretical sciences straddle most noticeably between philosophy and science.