It has its vacationist side (3)
I believe the answer is:
sea
'vacationist side' is the definition.
The definition and answer can be both natural objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'it has its' is the wordplay.
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'has' is an insertion indicator.
'its' becomes 'e' (I am not sure about this - if you are sure you should believe this answer much more).
'sa' placed around 'e' is 'SEA'.
Can you help me to learn more?
(Other definitions for sea that I've seen before include "Adriatic, for example" , "It's stocked with fish" , "Body of saltwater" , "Expanse of salt water" , "The Med, e.g." .)