Sing (5)
'sing' is the definition.
(I know that croon is a kind of sing)
This is all the clue.
(Other definitions for croon that I've seen before include "Sing softly" , "Sing like Bing" , "Sing with a soft voice" , "Sing in a soft low tone" .)
(Other definitions for along that I've seen before include "Beside - as groups often sing!" , "Sea monster, opposite Charybdis" , "Throughout; onward" , "Moving in a constant direction on (something)" , "With a forward motion: in accompaniment" .)
'sing' is the definition.
(I know that sing is a is a kind of of warble)
This is all the clue.
(Other definitions for warble that I've seen before include "Trill, yodel" , "Sing with gentle trilling note like some birds" , "Sing like a thrush" , "Sing - type of fly" , "Sing with trilling note like a bird" .)