The word "姑姑" is formed by duplicating the character "姑", which means "paternal aunt". This reduplication creates a direct address term for one's father's sister, used in familiar contexts. The character "姑" itself combines the radical "女" (woman) with the phonetic component "古" (gǔ), denoting its sound and associating it with female kinship. The repetition does not alter the core meaning but reinforces it as a term of address.