Ambience? A most peculiar piano in this place (10)
I believe the answer is:
atmosphere
'ambience?' is the definition.
(synonyms)
'a most peculiar piano in this place' is the wordplay.
'peculiar' is an anagram indicator (a peculiar or strange ordering of the letters).
'piano' becomes 'p' (musical abbreviation).
'in this place' becomes 'here' (synonyms).
'most' anagrammed gives 'tmos'.
'a'+'tmos'+'p'+'here'='ATMOSPHERE'
(Other definitions for atmosphere that I've seen before include "climate" , "Surrounding ambience" , "Gas surrounding a planet" , "Spirit" , "We are always enveloped in this" .)