With thanks to service, William first at peasant dance (10)
I believe the answer is:
tarantella
'peasant dance' is the definition.
'tarantella' can be an answer for 'dance' (tarantella is a kind of dance). I am not sure about the 'peasant' bit.
'with thanks to service william first at' is the wordplay.
'with' says to put letters next to each other.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'to service' becomes 'ran' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'william' becomes 'tell' (I've seen this before).
'first at' becomes 'a' (rst letter of 'at').
'ta' next to 'ran' is 'taran'.
'taran'+'tell'+'a'='TARANTELLA'
Can you help me to learn more?
(Other definitions for tarantella that I've seen before include "Lively Italian dance" , "furious dance" , "Lively Neapolitan dance" , "merry dance" , "dance music" .)