"tiil" is a riiksh word, with riiksh being one of the conlangs i made for my extremely hard to explain worldbuilding project called MMIN that ive been working on in some form or other since i was 15. ive written bits in it at times
(this project is also where ata and LIRU (=Left-Indigo Red-Up) are from)
so: what does the word mean?
the best single-word translation i can come up with is "cognophony" (portmanteau of "cognition" and "cacophony"); it is the noise that is thought
this in isolation probably doesn't really explain anything, so with that in mind, let me zoom out a bit
the original "world" a lot of the pov-characters have as their ancestral origin is called Seip. Seip is not a planet, there are no planets in the setting, or stars for that matter, the structure of space and behaviour of gravity-equivalents is different. but for now, just interpret it as a planet, for ease of conceptualisation
at the time before it's obliteration, there were 4 types of mind present on Seip that qualify as "people". 3 of those could also be categorised under the umbrella "sophont species", but the 4th (oldest) type cannot
that would be the zetiil (riiksh plural of tiil, prefix-ways), who exist as ancient swarm-intelligences with complex polyphonic "whistling" in place of neurotransmitter interaction. the individual creatures (not technically animals but again, ease of conceptualisation) are called "pèga", and they're visually somewhere in-between a bat and a grasshopper with the intelligence of an individual pèga being in the songbird-range
crucially this "whistle" and the interaction and reaction to its pitch and velocity and volume and density of sources etc is where the tiil is, not the pèga individuals as such
which is to say anything that can run the pattern can be a tiil, and indeed, even before the obliteration of seip, one of the 3 sophont species (the zezast (singular: zast)), being ancestrally good at imitating sounds, are often *part* of a tiil, and later after the scattering there's even examples of zast-only zetiil with no pèga involved at all!
TLDR; so what's a tiil?: imagine something between a locust swarm and a giant flock of birds. now imagine that swarm was a person. now imagine that as individuals within that swarm die and new ones are added it remains the same person for millennia upon millennia. that intelligence, that ancient mind of noise and motion. that's a tiil