Sign of Four : taken aback by reading work (5)
I believe the answer is:
virgo
'sign' is the definition.
(Virgo is an example)
'four taken aback by reading work' is the wordplay.
'four' becomes 'iv' (roman numeral).
'taken aback' is a reversal indicator.
'by' is a charade indicator (letters next to each other).
'reading' becomes 'r' (one of the traditional three R's of education).
'work' becomes 'go' ('go' can be a synonym of 'work').
'iv' written backwards gives 'vi'.
'vi'+'r'+'go'='VIRGO'
'of' acts as a link.
(Other definitions for virgo that I've seen before include "number of stars" , "House" , "Maiden" , "Star sign" , "Large constellation between Leo and Libra" .)