So, definitions, insofar as it works in my idiolect:
seeble, transitive verb [humorous mock-backformation from sibling, brother or sister]: To have a (gender-nonspecific) sibling relationship with the subject, particularly in the metaphorical sense of sharing the same feelings about the current topic of discussion and/or supportiveness and feeling sympathy.
seeble, interjection [from transitive verb seeble]: An expression that one seebles the person one is replying to.
Crossposted from Dreamwidth (original here), with comments. Comment here or there; comments here will eventually be duplicated to there.