Final answer:
The word 'tranquil' is most similar in meaning to 'peaceful'. 'Serene' is also closely related but 'tranquil' is a more direct synonym. 'Turmoil' represents confusion and 'quiet' the absence of sound.
Step-by-step explanation:
The word most similar in meaning to 'peaceful' among the options provided is tranquil. Both 'peaceful' and 'tranquil' imply a state of calm and quietness without disturbance. While 'serene' also carries a similar connotation and is closely related, 'tranquil' is typically cited as a direct synonym for 'peaceful'.
In contrast, 'turmoil' is quite the opposite as it denotes a state of confusion or disorder, and 'quiet', though related, refers more specifically to the absence of sound rather than an overall sense of peace.