Mistakenly hears these can’t get off the ground (5)
I believe the answer is:
rheas
'these can't get off the ground' is the definition.
The definition suggests an adverb but the answer is not.
'mistakenly hears' is the wordplay.
'mistakenly' is an anagram indicator.
'hears' with letters rearranged gives 'RHEAS'.
Can you help me to learn more?
(Other definitions for rheas that I've seen before include "Ostrich-like birds" , "Flightless birds" , "these birds won't fly" .)