Planet's environment agreeably receptive to humans ... initially (5)
I believe the answer is:
earth
'planet's' is the definition.
(Earth is an example)
'environment agreeably receptive to humans initially' is the wordplay.
'initially' indicates taking the first letters.
The initial letters of 'environment agreeably receptive to humans' is 'EARTH'.
(Other definitions for earth that I've seen before include "Lair; planet" , "Soil; ground terminal" , "Third rock from the Sun" , "our home" , "World - soil" .)