A Very Feminine Adjective
θῆλυς θῆλεια θῆλυ
Some adjectives combine the features of the First and Third Declension particularly those with u stems like this one θῆλυς θῆλεια θῆλυ which means female, of female sex, feminine, belonging to women, tender, delicate, nourishing, and sometimes effeminate.
The Masculine and Neuter are declined like ἄστυ but the feminine is declined like a First Declension adjective ending in α.
So Masculine and Neuter Singular
Nominative θῆλυς Accusative θῆλυν Genitive θῆλέος Dative θηλεῖ
The Classics example is the declension of γλυκύς which you can see in Goodwin's Grammar Pages 67-8 or in whichever Grammar you are using as a reference for further details.
There are however some minus differences between θῆλυς θῆλεια θῆλυ and γλυκύς.
Note how the genitive singular ends in - ος and the – έα Neuter Plural with both Adjectives.
θῆλεια has more differences in the accusative forms. The Epic and Ionic forms end in α instead of ια so that θήλεα θεός is a goddess.
The original feminine ending of this adjective and possibly of the other genders may have been – eu or ewo changing and contracting to u in one gender and eu then e in the other.
It seems off that there would be a masculine and neuter at all but there exists such phrases as θήλειαι ἵπποι meaning mares or female horses and τὸ θῆλυ the female (gender).
Some other u- stem adjectives that follow the γλυκύς pattern are:
βραχύς short brief εὐρύς broad wide ἡδύς sweet pleasant pleasing
ἥμισυς half ὀξύς pointed sharp ταχύς swift fast