My favorite is sex and gender.  I can see where hand-powered excavation
device is synonymous with spade.  Erectile dysfunction isn't as descriptive
as impotence.  But, gender does no equal sex.  Gender has to do with
language and, now that I am thinking of it, does not come into play in the
English language.  The gender of "amiga" is feminine.  That of "amigo" is
masculine.  I guess the gender of the word "female" is feminine -- I 'd have
to find an English scholar to tell me.  But "female" is a sex and "male" is
a sex.

Stepping off the soapbox