One can't fly after Heathrow's blocked (4)
I believe the answer is:
rhea
'one' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'can't fly after heathrow's blocked' is the wordplay.
'RHEA' is hidden in amongst the letters.
But, I'm unsure how the hidden word is indicated.
Can you help me to learn more?
(Other definitions for rhea that I've seen before include "South American bird resembling the ostrich" , "China grass" , "S American runner" , "Flightless bird -- satellite of Saturn" , "Greek goddess of fertility - running bird" .)