Further to my previous post (kind of):
People tend to refer to it as “kisses” when an animal licks a person or another animal, so I’ve always run on the assumption that when cats groom each other it’s an act of affection. But apparently not always.
Back in August or so, I got a kitten to keep Bastardcat company. I shall refer to her as Dickface.
When Dickface first became part of our family and Bastardcat got over his initial WTF reaction to her, he would groom her sometimes – but it was very clearly an act of dominance. Usually they’d be playfighting and he’d pin her down and start licking her face (or her asshole. There was a lot of forced analingus in the early days). It was very much a show of power, like when a bully pins a smaller kid down and does that almost-spitting-but-sucking-it-back-up thing over their face: Bastardcat was showing Dickface that he was bigger than her and capable of infantilizing her whether she consented or not.
Sometimes, back then, she would try to groom him. Always very tentatively, and always by sneaking up behind him while he was asleep. She’d give his ear a few licks and he’d growl at her for being presumptuous.
At some point, things shifted. Bastardcat went from politely tolerating Dickface the Kitten to actually liking her. So now sometimes she’ll groom him and he’ll lie back with a huge smile on his face like “Yesssss. Wash me, peon.” Or they’ll cuddle up and groom each other simultaneously.
Throughout all of this, Dickface has occasionally had times where she felt really submissive (missing being babied by her mother, I’m guessing) and would crawl over to Bastardcat with her head stretched out flat and a big Bambi-eyed expression, soliciting a grooming from him.
tl;dr: cats are fucking adorable and the same exact action can be used for many different purposes and dynamics.