Charlie in tartan not easily ruffled (6)
I believe the answer is:
placid
'not easily ruffled' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives can occasionally define each other.
'charlie in tartan' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' indicates putting letters inside.
'tartan' becomes 'plaid' (synonyms).
'c' placed inside 'plaid' is 'PLACID'.
Can you help me to learn more?
(Other definitions for placid that I've seen before include "Calm and still" , "Calm, unruffled" , "Peaceful - composed" , "without ruffles" , "Calm; equable" .)