gender vs feminineness

gender and feminineness both are nouns.

Word	Noun	Adjective	Verb	Adverb
gender	Yes	No	No	No
feminineness	Yes	No	No	No

As nouns, feminineness is a hyponym of gender; that is, feminineness is a word with a more specific, narrower meaning than gender:

gender: the properties that distinguish organisms on the basis of their reproductive roles
feminineness: the properties characteristic of the female sex

Other hyponyms of gender include maleness, masculinity, androgyny, bisexuality, hermaphroditism, femaleness.

gender (noun)	feminineness (noun)
the properties that distinguish organisms on the basis of their reproductive roles	the properties characteristic of the female sex
a grammatical category in inflected languages governing the agreement between nouns and pronouns and adjectives; in some languages it is quite arbitrary but in Indo-European languages it is usually based on sex or animateness