[ColinWright]

> The reciprocal, on the other hand, is very clearly understood to be the quotient such that the nominator and denominator are reversed.

That depends on the math you use. In this case you are given a floating point argument, so there really isn't a concept of reciprocal either, because it's not a rational number. There are places where "reciprocal" is not specific to the rationals, but there it is usually a more general term meaning pretty much the same as inverse.

In both cases context is everything, and trying to read this - as with all math - in isolation is likely, almost inevitable, to cause confusion.

In this case it's the multiplicative inverse of the square root of the argument.