Final answer:
The term for a 'wild hawk captured after it had already grown its mature feathers' is a haggard, which comes from the falconry practice of capturing adult birds of prey, known to be more challenging to train due to their wild instincts.
Step-by-step explanation:
The term you're looking for, which defines a 'wild hawk captured after it had already grown its mature feathers,' is known as a haggard. This term has its roots in falconry, where a haggard refers to an adult bird that has developed its full plumage and has lived in the wild before being captured. Unlike a bird taken from its nest before it could fly, which is known as an eyas, a haggard may be more challenging to train due to its established wild instincts and behaviors.
Examples of haggards can often be seen in literature where birds of prey or hawks are depicted in their mature, wild state, evocative of freedom and untamed nature. The emergence of such a term into the English language shows the historical relevance of falconry, as well as the fascination and respect for these majestic birds of prey.