Abarim Publications' online Biblical Hebrew Dictionary
אנא
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.
Our particle is a combination of the common exclamation of grief, אח ('ah), and the common particle of entreaty נא (na), which makes it related to the more familiar expression Hosanna.