3rd declension adjectives in  -υς, εια, υ 

singular	nom				plural	nom		ες	α neuter
	gen		ος			gen		ων
	dat		ι			dat		σι
	acc		α			acc		ας	α neuter

Little flies in the ταχύς, ταχέος ointment:

Nominative and accusative plural both do contract, to:  -εῖς 
Accusative masculine singular ends in -ν not -α 

ὁ ταχὺς ἵππος 

singular nominative   ὁ   ταχύς  ἵππος τρέχει ταχέως genitive ὁ δεσπότης τοῦ   ταχέος  ἵππου hopes it will win the race dative   τῷ   ταχεῖ  ἵππῳ χαίρει ὁ ἄγγελος accusative ἐπὶ τὸν   ταχὺν  ἵππον ἀναβαίνει ὁ ἱππεύς plural nominative   οἱ   ταχεῖς  ἵπποι καλοί εἰσιν.  genitive ὁ ἀγὼν τῶν   ταχέων  ἵππων is a splendid sight dative ἐπὶ   τοῖς  ταχέσιν  ἵπποις ἐκ κινδύνου φεύγουσιν. accusative τοὺς  ταχεῖς  ἵππους θαυμάζομεν

τὸ ταχὺ ζῷον 
   Regular 3rd declension endings:
   τὰ ταχέα ζῷα ταχέως τρέχει 

ἡ ταχεῖα ἅμαξα, τῆς ταχείας ἁμάξης ....
   feminine form like for any other 1st declension adjective.