Abarim Publications' online Biblical Hebrew Dictionary
The particle אנא ('anna') is a kind of fortified exclamation of grief, roughly translatable with "ah, now!" or "we beseech thee!" (Genesis 50:17, Exodus 32:31, Psalm 118:25).
On a few occasions this particle is spelled אנה, which makes it look like a nod towards the verb אנה ('ana I), meaning to mourn.