In casual manner noble at outset only accepting tea, left walnuts regularly? (12)
I believe the answer is:
nonchalantly
'in casual manner' is the definition.
(nonchalantly matches up with the definition in casual manner)
'noble at outset only accepting tea left walnuts regularly?' is the wordplay.
'at outset' suggests taking the first letters.
'accepting' means one lot of letters goes inside another (inserted letters are accepted).
'tea' becomes 'cha' (cha is a type of tea).
'left' becomes 'l' (common abbreviation).
'regularly?' means one should take alternating letters (regularly take one letter, leave next etc.).
The initial letter of 'noble' is 'n'.
The alternate letters of 'walnuts' are 'ant'.
'cha'+'l'+'ant'='chalant'
'only' placed around 'chalant' is 'onchalantly'.
'n'+'onchalantly'='NONCHALANTLY'
(Other definitions for nonchalantly that I've seen before include "in casual fashion" , "In insouciant fashion" , "With composure" , "Casually taking" , "In a calm and relaxed manner" .)