The opposite gender of giantess is giant.
Sorry, 'giant' does not denote or connote gender at all.
The 8-letter "opposite gender" of a male giant is "giantess." (There is no common 8-letter antonym to a giant or to the adjective giant.)
Doctor is a neuter gender
Opposite gender of Filipino: Filipina
Clot is not gender specific.
Opposite gender of a Filipino: FILIPINA
The opposite gender of farmer is farmeress or farmwife.
The opposite gender of fraternity is sorority.
The opposite gender for Joseph is Josephine.
An emperor is the opposite in gender to an empress.
The opposite of dairymaid is dairyman.