http://dictionary.reference.com/browse/main
http://www.reference.com/browse/wiki/Hippopotamus
You counter with nonsense. And no the I'm playing now isn't the one I care most about, that's like saying my main job at work is the one i'm doing which is total BS.
Another fail on your part is saying there is no toon you care most about and then following with, ofc you do it's the one you're playing now.
There are various ways of determining what toon is your main, you can use /age, amount of exo's, the one you enjoy most,... The concept of main isn't grabbed out of thin air, ppl simply have other parameters to determine what toon is their main.