Gas - the name is peculiar (7)
I believe the answer is:
methane
'gas' is the definition.
(methane is a gas)
'the name is peculiar' is the wordplay.
'is peculiar' indicates an anagram (a peculiar or strange ordering of the letters).
'the'+'name'='thename'
'thename' anagrammed gives 'METHANE'.
(Other definitions for methane that I've seen before include "Marsh gas - the name (anag)" , "Marsh-gas" , "Flammable gas, CH4" , "Greenhouse gas produced by cows" , "Combustible atmosphere" .)