äitiinsä
äitiinsä is a Finnish noun phrase formed from äiti (mother) plus the third-person possessive suffix -nsä, traditionally yielding the meaning “his/her mother.” In standard Finnish, the correct written form is vaak in practice äitinsä, with the possessive suffix attaching directly to the stem and producing a single i before the suffix. The form äitiinsä, with two consecutive i’s, is not considered standard and is generally viewed as a nonstandard spelling or typographical error. Some older texts or dialectal writings may show such variants, but äitinsä is the form used in contemporary standard Finnish.
Usage of äitinsä follows the general possessive construction in Finnish. It denotes that the mother belongs
Etymology and structure: äiti is the root meaning mother, and -nsä is the 3rd person singular possessive
See also: Finnish possessive suffixes, Finnish grammar, äiti.