Hag humorist joins church (5)
I believe the answer is:
witch
'hag' is the definition.
(synonyms)
'humorist joins church' is the wordplay.
'humorist' becomes 'wit' (wit is a kind of humorist).
'joins' says to put letters next to each other.
'church' becomes 'ch' (abbreviation on maps etc).
'wit'+'ch'='WITCH'
(Other definitions for witch that I've seen before include "One supposed to have magical powers" , "Bad speller!" , "Female member of coven" , "strange woman" , "Wise, wicked, woman" .)