Come again, though only occasionally (3)
I believe the answer is:
huh
'come again' is the definition.
(both are used to ask someone to repeat something)
'though only occasionally' is the wordplay.
'only occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternating letters of 'though' are 'HUH'.
(Other definitions for huh that I've seen before include "sorry?" , "Expression of disgust or surprise" , "Palindromic exclamation of disgust or surprise" .)