Lobby organisation's initial greeting (5)
I believe the answer is:
hallo
'greeting' is the definition.
(I've seen this before)
'lobby organisation's initial' is the wordplay.
'lobby' becomes 'hall' ('hall' can be a synonym of 'lobby').
'initial' suggests taking the first letters.
The first letter of 'organisation' is 'o'.
'hall'+'o'='HALLO'
(Other definitions for hallo that I've seen before include "First indication" , "greeting" , "I say" , "welcoming for visitors?" , "Word welcoming" .)