The word "天竺" is formed through phonetic borrowing, where the characters "天" (tiān) and "竺" (zhú) are used solely for their sounds to approximate the historical foreign name for India, derived from sources like Sanskrit "Sindhu" via intermediary languages. The individual meanings of the characters, "heaven" or "sky" for "天" and "bamboo" or a historical reference for "竺", are not relevant to the word's formation, as it functions as a transliteration.