Screw, small, fairly regularly used (6)
I believe the answer is:
salary
'screw' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'small fairly regularly used' is the wordplay.
'regularly used' means one should take alternating letters (letters selected on a regular basis).
'small'+'fairly'='smallfairly'
The alternate letters of 'smallfairly' are 'SALARY'.
Can you help me to learn more?
(Other definitions for salary that I've seen before include "Remuneration for work done" , "Annual pay" , "Fixed regular payment of work" , "Regular income from employment" , "Remuneration for Ray and Sal" .)