No convincing explanation of the loss of the initial *h has been suggested. The deictic extension *-tī has parallels in other pronominal forms (for example, Geez zātti). See Bulakh–Kogan 2013b:98.
The form results from the extension of the sg. pronoun by the pronominal enclitic of the oblique case. Its origin is, thus, secondary (Kogan 2009:68). See ˀəmmāntu, the other Geez pronoun with the meaning “they (fem.)”.