select myword from mytable;

myword
dark
darkness
darked
darks
DARK
goat
tin can
dark sun
DarkAges
darkage
my dog sunshine

(11 rows)

select myword from mytable where myword = 'dark';

myword
dark

(1 row)

select myword from mytable where myword = 'dark' or myword='darkness';

myword
dark
darkness

(2 rows)

select myword from mytable where myword ~ 'dark' or myword='darkness';

myword
dark
darkness
darked
darks
dark sun
darkage

(6 rows)

select myword from mytable where myword ~* 'dark' or myword='darkness';

myword
dark
darkness
darked
darks
DARK
dark sun
DarkAges
darkage

(8 rows)