Why is ᾗ feminine?

Greek Learning Greek
1

ᾗ , dat. sg. fem. of relat. Pron. ὅς, ἥ, ὅ, in adverb. sense,

  1. [select] of Place, which way, where, whither, relat. to τῇ,…

I thought it was only neuters that got used adverbially. Are there any other, more common than this one, adverbs derived from feminine forms?

Thanks in advance

2

Not sure if they’re more frequent than ῇ, but Mastronarde lists a couple of others in the section on correlatives (unit 36): πῇ (by which way?, where?), πῃ (in some way), τῇδε, ταύτῃ (in this way, by this way), ᾗ (in which way, as) and ὅπῃ (in which way, as). τῇ appears in brackets and paired with τῇδε and ταύτῃ in Goodwin (§436).

3

The formally dative feminine adverbs probably originated by ellipsis of ὁδῷ.