Really funny greeting - different opening is ten times bigger (9)
I believe the answer is:
hilarious
'really funny' is the definition.
'hilarious' can be an answer for 'funny' (I've seen this before). I am not sure about the 'really' bit.
'greeting different opening is ten times bigger' is the wordplay.
I cannot quite understand how this works, but
'greeting' could be 'hi' (hi is a kind of greeting) and 'hi' is found within the answer.
'ten' could be 'io' (IO resembles 10) and 'io' is present in the answer.
The remaining letters 'larus' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hilarious that I've seen before include "Extremely amusing" , "Uriah's oil (anag.)" , "Louis' hair! (anag)" , "A scream" , "Extremely funny" .)