What an uninvited guest may do under it, possibly (7)
I believe the answer is:
intrude
'what an uninvited guest may do' is the definition.
The definition suggests a singular noun but the answer is not.
'under it possibly' is the wordplay.
'possibly' is an anagram indicator.
'under'+'it'='underit'
'underit' with letters rearranged gives 'INTRUDE'.
Can you help me to learn more?
(Other definitions for intrude that I've seen before include "Come in when not wanted" , "Because of temperature, blue" , "Gatecrash" , "Pry" , "Come in without invitation" .)