Host returned to assist worker on farm (9)
I believe the answer is:
dairymaid
'worker on farm' is the definition.
'dairymaid' can be an answer for 'worker' (dairymaid is a kind of worker). I'm not certain of the 'on farm' bit.
'host returned to assist' is the wordplay.
'host' becomes 'myriad' (I've seen this before**).
'returned' is a reversal indicator.
'to assist' becomes 'aid' ('aid' can be a synonym of 'assist').
'myriad' back-to-front is 'dairym'.
'dairym'+'aid'='DAIRYMAID'
Can you help me to learn more?
(Other definitions for dairymaid that I've seen before include "Worker with milk, butter, etc" , "Woman who milked cows" , "Girl perhaps making butter or cheese" , "Midday air (anag.)" , "old farm worker" .)