Important greeting reaching ears (4)
I believe the answer is:
high
'important' is the definition.
(thesaurus)
'greeting reaching ears' is the wordplay.
'greeting' becomes 'hi' (hi is a kind of greeting).
'reaching ears' becomes 'gh' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'hi'+'gh'='HIGH'
Can you help me to learn more?
(Other definitions for high that I've seen before include "Shrill" , "Over-excited" , "Anticyclone; euphoric" , "Western film with Gary Cooper" , "Elevated; euphoric" .)