Speed like the flying swallows (5)
I believe the answer is:
haste
'speed' is the definition.
(I know that haste is a type of speed)
'like the flying swallows' is the wordplay.
'like' becomes 'as'.
'flying' indicates anagramming the letters (letters fly around into new positions).
'swallows' indicates putting letters inside.
'the' is an anagram of 'hte'.
'as' inserted into 'hte' is 'HASTE'.
(Other definitions for haste that I've seen before include "The more of it, the less speed, it is said" , "Urgent hurry" , "Promptitude" , "Undue speed" , "dispatch" .)