Fear of not having a right arm? (5)
I believe the answer is:
alarm
'fear' is the definition.
(alarm is a kind of fear)
'of not having a right arm?' is the wordplay.
'of not' becomes 'alar' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'having' says to put letters next to each other.
'a right' suggests the final letters (I've seen 'right of' mean this (letter on the rightmost end of the word)).
The final letter of 'arm' is 'm'.
'alar'+'m'='ALARM'
Can you help me to learn more?
(Other definitions for alarm that I've seen before include "Warning siren" , "Alternative to reveille" , "Noise that wakes" , "Agitate" , "Security device" .)