Advertisement says electricity’s initially included in rent (6)
I believe the answer is:
teaser
'advertisement' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'says electricity's initially included in rent' is the wordplay.
'initially' indicates taking the first letters.
'included in' indicates putting letters inside.
'rent' becomes 'tear' (synonyms).
The first letters of 'says electricitys' is 'se'.
'se' put inside 'tear' is 'TEASER'.
Can you help me to learn more?
(Other definitions for teaser that I've seen before include "A difficult problem of Teresa" , "Hard question" , "One who irritates playfully" , "inducement" , "One who annoys people or cards wool" .)