Slave (6)
'slave' is the definition.
(I know that Thrall is a type of slave)
This is the entire clue.
(Other definitions for thrall that I've seen before include "subjection" , "captivity" , "Slave(ry)" , "In . . . . . . means in bondage" , "Slave, servant, captive" .)
'slave' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for menial that I've seen before include "Domestic servant" , "Unskilled, degrading" , "Servile, low" , "(Suitable for) servant of low status" , "Servile and humiliating" .)