Eur., El., 45

ἣν οὔποθ᾽ ἁνὴρ ὅδε — σύνοιδέ μοι Κύπρις —
ᾔσχυνεν εὐνῇ: παρθένος δ᾽ ἔτ᾽ ἐστὶ δή.
Is it possible to say from the context in such cases whether this is an impf or ao: ᾔσχυνεν ?

That context would make it look like a single act being denied.

i think it is as ambiguous as in english, so either impf or ao

The English would be something like: “This man never – Kypris knows – shamed her by the bed. She is still a virgin, certainly.”

I don’t see how that is ambiguous as to tense in English (and the same for the Greek).

(Yes, “by the bed” is Greeklish. It’s referring to an act of copulation. I didn’t use more idiomatic English, because I didn’t want to warp the sentence too much.)

ok probably ur right

I think οὔποτε forces a perfective translation, which would mean aorist. Does the meter help here? The lexicons seem a bit confused over the quantity of the stems, but if the imperfect stem shortens, and the aorist is long…

The upsilon is long both in the present stem and in the aorist stem. (The lexica are not “confused.”) So it’s one of those verbs that are identical in form in 3 sing. aor. and impf. That’s often the case with sigmatic aorists where the sigma is phonologically suppressed (e.g. after nu, as here), cf. e.g. krinw.
In context there’s rarely any real ambiguity. Here it’s obviously aorist.