sister: a female relative by blood or kinship, from full sister to half-sister and broader female kin
The basic and overwhelmingly dominant sense of achot is the female counterpart of ach (brother): a woman who shares one or both parents with another person. The word covers both full sisters and half-sisters with no distinction in form. In Leviticus the incest laws repeatedly invoke this term to define prohibited relationships: one's sister (daughter of father or mother), one's father's sister, one's mother's sister (Lev 18:9, 12, 13).
The term extends naturally to broader female kinship. In Numbers 25:18 Cozbi is called "their sister," meaning a kinswoman of the Midianites. In Leviticus 18:18 the phrase "a woman alongside her sister" (אִשָּׁה אֶל אֲחֹתָהּ) designates a co-wife or rival, using the word for any woman paired in the same marital bond. This broader-kin range is consistent with ach (brother), whose own range extends from brother to kinsman.
Geneaological notices throughout the Hebrew Bible routinely name female members of clans and tribes with this word (1 Chr 2:16; 3:9; 7:15, 18, 30, 32 and many others), confirming its standard role as the feminine noun for a family's female line.