Arrival by alien going around Earth (5)
I believe the answer is:
terra
'earth' is the definition.
(thesaurus)
'arrival by alien going around' is the wordplay.
'arrival' becomes 'arr' (abbreviation used in transport).
'by' means one lot of letters go next to another.
'alien' becomes 'et' (extra terrestrial).
'going around' says the letters should be written backwards.
'arr'+'et'='arret'
'arret' written backwards gives 'TERRA'.
(Other definitions for terra that I've seen before include "Centre" , "Land (Latin)" , "Legally land" , "Latin word for earth" , "Dry land" .)