ἥσυχος, ἥσυχον: quiet, at rest; secure, untroubled

singular      plural
      masculine 
 feminine 
    neuter           masculine 
 feminine 
    neuter    
 nom    ἥσυχ ος       ἥσυχ ον       nom    ἥσυχ οι       ἥσυχ α    
 gen  ἡσύχ ου    gen  ἡσύχ ων  
 dat  ἡσύχ ῳ    dat  ἡσύχ οις  
 acc  ἥσυχ ον       ἥσυχ ον     acc  ἡσύχ ους       ἥσυχ α  
 voc  ἥσυχ ε       ἥσυχ ον     voc  ἥσυχ οι       ἥσυχ α  
 
 
 
 Note: 

Some adjectives in -os are used both for masculine and for feminine nouns. Most, though not all, are compounds like: un-happy, well-doing, a-moral etc.

Some examples are:
unending, lesson 1a: τέλεστος, ον
endless, lesson 1a (new version): πέραντος, ἀπέραντον
(not shirking) = energetic, (lesson 1a) : οκνος, ἄοκνον from ὀκνεῖ he shirks (lesson 1b, supplementary reading: Ο ΚΛΗΡΟΣ)
not working, idle, lazy, lesson 2a: ργός, ἀργόν, idle, lazy (made up from (=not) and ἔργον (=work)
fool, mindless, lesson 3a: νόητος, on (from ὁ νοῦς, ἐν νῷ ἔχω, I have in mind, intend)
impossible: δύνατος, ον
fully armed, in arms, lesson 9a: ἐνόπλιος, ον
immortal,θάνατος, ον

'Quiet' ἥσυχος, ἥσυχον is another one of them, though not a compound. Think of people or places that are 'quiet'