Use of "inverse" to mean reciprocal Oftentimes I hear people referring to reciprocals as in this example:

The slopes are negative inverses, so the lines are perpendicular to each other.

This always confuses me because the word "inverses" seems overly general to refer to reciprocals in particular.
Is this common usage ever correct, or is "reciprocal" always a better word to use?
 A: I cannot think of an instance where "inverse" by itself is a better choice than "reciprocal" if you are discussing a reciprocal.  Of course, "multiplicative inverse" is just as good as "reciprocal."
A: The word inverse needs a context.   People often use it alone when they think the context is clear.  There are additive inverses, multiplicative inverses and compositional inverses to name a few.  
Yes, there is some ambiguity there.
A: In the context of functional iteration we have "the inverse" which means then the functional inverse, $f^{-1}(x)$ for instance $\sin(x)$ and $\arcsin(x)$ while "the reciprocal" means $1/f(x)$.    
In the context of matrices of infinite size the inverse should always be called "reciprocal" - if I recall right; I think the reason given was some indeterminacy, for instance we can have two infinite matrices M1 and M2 which give the (infinite) unit-matrix when right-multiplied with some other matrix X: $M1*X = M2*X=I$  (But I don't have the source of that recommendation at hand)
A: A reciprocal is something that, when multiplied by the given number, leads to a product of 1. Ditto for a type of inverse known as a MULTIPLICATIVE inverse. (And a "negative reciprocal" gives you a -1).
