OED

Oxford English Dictionary

Bachelor-

• The first citation of the word bachelor was recorded in 1297 in 'The Chronicle of Robert of Gloucester '.
• It originally comes from France or Italy.
• The primary meaning of the word is 'A young knight, not old enough, or having too few vassals, to display his own banner, and who therefore followed the banner of another; a novice in arms', therefore, it has always been a gender specific word for a male.
• Overtime, the meaning of the word has widened and has now become known as 'an unmarried man (of marriageable age)'.
• The original spelling of the word has deviated from 'bacheler' and 'bachelere'.

Slut-

• The first citation of the word in 1402 in a novel.
• The etymology hasn't been confirmed but it is most likely Germanic.
• Its original meaning is 'A woman of dirty, slovenly, or untidy habits or appearance; a foul slattern.'
• It has now pejorated and has become a word to describe a woman who sleeps around.

• This shows that it has always been gender specific to women.
• There has been no spelling changes.

Stud-

• The first citation of this word was in c1000
• It originally meant, 'An establishment in which stallions and mares are kept for breeding'
• The etymology is Old English.
• It has no broadened in meaning, 'A man of (reputedly) great sexual potency or accomplishments; a womanizer, a habitual seducer of women'.
• The connotations of these words have ameliorated, as a man who is described as a stud has become admirable for having 'many women on the go', which is what men now aspire to rather than monogamy.

Witch-

• This word was originally used to describe a Man who practises witchcraft.
• The meaning has changed to represent a woman.
• The semantic meaning is the same, however, the connotations of a woman witch are negative. e.g. evil, old, ugly etc.

Wizard-

• This is the male equivalent to 'witch', it describes a 'magical' man.
• Although the semantic meaning is the same to witch, Wizard has more positive connotations e.g. powerful, wise etc.