The second stanza of Sappho's Poem 16 is reconstructed as follows:
πάγχυ δ' εὔμᾱρες σύνετον πόησαι
πάντι τοῦτ', ᾱ γὰρ πόλυ περσκέθοισα
κάλλος ἀνθρώπων Ἐλένᾱ τὸν ἄνδρα
I'm mostly familiar with Attic, but trying to branch out into other dialects. Most of the unfamiliar Aeolian words are fairly easy to figure out: for instance, πόησαι is Attic ποίησαι, and ᾱ is Attic ἡ.
But I'm unsure what to do about περσκέθοισα. LSJ lists no stems starting with persk-, nor with peri-sk-. What word does this come from? And what form is it?