soporific
adjective /ˌsɒpəˈrɪfɪk/
  /ˌsɑːpəˈrɪfɪk/
(formal)- making you want to go to sleep
- the soporific effect of the sun
 
Wordfinder- doze
 - dream
 - drowsy
 - insomnia
 - oversleep
 - REM
 - sedative
 - sleep
 - soporific
 - tired
 
Oxford Collocations DictionarySoporific is used with these nouns:- effect
 
Word Originmid 17th cent.: from Latin sopor ‘sleep’ + -ific.