Top sovereign put on good plane (6)
I believe the answer is:
glider
'plane' is the definition.
(glider is a type of plane)
'top sovereign put on good' is the wordplay.
'top' becomes 'lid' (lid is a kind of top).
'sovereign' becomes 'er' (Abbreviation for Elizabeth Regina).
'put on' means one lot of letters go next to another (some letters go on or after others).
'good' becomes 'g' (abbreviation).
'lid'+'er'='lider'
'lider' after 'g' is 'GLIDER'.
(Other definitions for glider that I've seen before include "Girdle for silent flier" , "Powerless aircraft" , "taking flight?" , "Aircraft supported solely by air" , "Unpowered plane" .)