Have you energy? Hurry! (5)
I believe the answer is:
haste
'hurry' is the definition.
(haste is hurrying or rushing)
'have you energy?' is the wordplay.
I cannot quite understand how this works, but
'energy?' could be 'e' (physics symbol as in E=mc2) and 'e' is found within the answer.
The remaining letters 'hast' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for haste that I've seen before include "Speediness or rush" , "Rushing (but with less speed?)" , "go at speed" , "impetuosity" , "Possible cause of careless mistakes?" .)