小母

From 小 (o, "little," "nice") + 母 (ba, "mother")(Can this⁽⁺⁾ etymology be sourced?)

小母 (hiragana おば, rōmaji oba)

1. endearing term for a woman who is unrelated to and older than the speaker (used with honorific -さん or -さま)
2. term used by a child to address an unrelated woman (used with honorific -さん)

• Often found in kana form: おば