The word 丫挺 is formed through the contraction and phonetic alteration of the phrase 丫头养的 (yā tou yǎng de), where 丫 abbreviates 丫头 and 挺 arises from a dialectal mispronunciation or slurring of 养的, specifically corrupting 养 (yǎng) into 挺 (tǐng) in colloquial usage.