Remember the basic 3rd declension endings, which will be added to the stem of the noun.

 
SINGULAR
  
 nominative             τὸ    ὄνομα   Πέτρα ἐστίν
 genitive   ὁ     τοῦ    ὀνόματος     meaning is "stone or rock"  
 dative   Ἀριάδνη      ὀνόματι    = by name 
 accusative   ἀγνοῶ     τὸ    ὄνομα     τοῦ βασιλέως.
 vocative     ὦ      ὄνομα    
  
PLURAL
  
 nominative           τὰ    ὀνόματα     χαλεπά ἐστιν
 genitive   ἡ μελῳδία     τῶν    ὀνομάτων     εὔφωνός ἐστιν.
 dative       τοῖς    ὀνόμασι     we distinguish people
 accusative   γιγνώσκομεν     τὰ    ὀνόματα     τῶν ἑλληνικῶν θεῶν  
 vocative     ὦ      ὀνόματα    
  
 
It is difficult to think of ways of using all these forms of τὸ ὄνομα .
But it is one of the easiest 3rd declension words, just note that in the dative plural the
τ is dropped in front of σι . As usual, for the sake of ease of pronunciation.

Other words that follow the same pattern. Note that they all end in -μα and are all neuter:

  • All the words in Practice in Writing and Pronunciation, page xi (xviii new edition) and
  • τὸ σπέρμα, τοῦ σπέρματος, seed, see lesson 3
  • τὸ ἕρμα, τοῦ ἕρματος, a pile (of stones for instance to mark a boundary), lesson 1b
  • τὸ θαῦμα, τοῦ θαύματος, marvel, wonder