Final answer:
The combining form 'tympan(o)' is related to the 'eardrum', an integral component of the auditory system responsible for the initial vibration in response to sound.
Step-by-step explanation:
The combining form tympan(o) is most closely associated with the tympanic membrane, which is better known as the eardrum. This membrane is a crucial part of the hearing apparatus, vibrating in response to sound waves, and is situated at the end of the auditory canal. The vibration of the eardrum is the first step in the mechanical process that leads to the perception of sound. Thus, the correct answer to the question of identifying the combining form tympan(o) with its closest definition is a. Eardrum.