Basically, in Finnish folklore, Ajatar (also spelled Aiatar, Ajattaro or Ajattara) is a spirit known as "Devil of the Woods". It is an evil female spirit that manifests as a snake or dragon.She spreads disease and pestilence, any that look at her become ill, and she suckles serpents. Ajatar is related to the Lithuanian Aitvaras and the Estonian Äi, Äijo or Äijattar. She is in some ways similar to Babylonian Tiamat, dragon mother of the gods and goddesses.

"ajatar" is possibly derived from the verb ajattaa, "make to pursue", of Finnish word ajaa , "to pursue". I think.

On the other hand "Ajatar" might also refer to (Finnish) word aika "time".