Host welcoming English man with his peculiar device (9)
I believe the answer is:
mechanism
'device' is the definition.
(I know that mechanism is a type of device)
'host welcoming english man with his peculiar' is the wordplay.
'host' becomes 'mc' (short for Master of Ceremonies).
'welcoming' indicates putting letters inside (in sense of 'inviting in').
'english' becomes 'E' (abbreviation).
'with' says to put letters next to each other.
'peculiar' is an anagram indicator (a peculiar or strange ordering of the letters).
'mc' enclosing 'e' is 'mec'.
'man' put after 'his' is 'hisman'.
'hisman' with letters rearranged gives 'hanism'.
'mec'+'hanism'='MECHANISM'
(Other definitions for mechanism that I've seen before include "Device with moving parts that performs some function" , "Way in which something works" , "Workings" , "Process" .)