Introduction of hike in rent is an irritation (5)
I believe the answer is:
thorn
'an irritation' is the definition.
(thesaurus)
'introduction of hike in rent' is the wordplay.
'introduction of' suggests taking the first letters.
'in' indicates putting letters inside.
'rent' becomes 'torn' (synonyms).
The first letter of 'hike' is 'h'.
'h' placed inside 'torn' is 'THORN'.
'is' is the link.
(Other definitions for thorn that I've seen before include "quill?" , "Prickly plant" , "Prickle on a plant" , "Plant spine; old letter" , "Sharp-pointed stem-tip" .)