Up in Idaho landlord's welcome (5)
I believe the answer is:
aloha
'welcome' is the definition.
(I've seen this before)
'up in idaho landlord's' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'in' indicates a hidden word.
'ahola' is hidden in the letters of 'idaho landlords'.
'ahola' backwards is 'ALOHA'.
(Other definitions for aloha that I've seen before include "Hawaiian greeting" , "A Polynesian hello or goodbye" , "Hi! in Honolulu" , "Hawaiian "ciao"" , "Welcome to Honolulu!" .)