/eva / एव

In a sUtra, eva एव means "only".

It is an enclitic. So "only a mouse" is mUSika::eva मूषिक‌एव. You cannot place /eva at the other end of the sentence, as if it were **kevalam केवलम्.

So in sUtra patissamAs... we hear:

samase समसे + eva एव → samAsa:: eva समास‌ एव "only in a compound"

In common Sanskrit it is used as an intensifier, to mean "indeed, verily, actually".

coras saH चोरः सः "he's a thief"

sa::eva coraH स‌एव चोरः "I'm positive that he's the thief"

cora::eva saH चोर‌एव सः "he's indeed a thief", "he's an actual thief"

In the epics often used as samasyApUraNa, a verse filler with no meaning. So in prose we should have a distinction of emphasis here —

mAdhavaH pANDavaz ca माधवः पाण्डवश्च "Krishna and Arjuna"

mAdhavaH pANDavaz caiva माधवः पाण्डवश्चैव "Krishna and Arjuna too"

But if that's from a verse you should leave the "too" out of the translation, it is just a filler.

In commentaries eva एव is often used as a focus marker. see wikipedia on Focus_(linguistics).

Teaching students to NOT translate eva एव as "verily", "certainly" or "surely" is quite hard. Students don't like leaving any word untranslated, and a "verily" sort of fits smoothly anywhere in any sentence.

Well, not just students. See prabhupAda प्रभुपाद for lots of examples like —

Or he takes his birth in a family of transcendentalists who are surely great in wisdom. Verily, such a birth is rare in this world