Out of curiosity, I've been looking at the various examples of Theyalan that can be found across various sourcebooks, specifically those which are given defined meanings, and trying to work out the rules and such behind them.
I'm posting what I've got here, in the hopes of A: it being interesting/useful to anyone else, and B: someone knowing something that I've missed, or having other thoughts that would improve things.
Guide to Glorantha
Argrath - Liberator (459) Mralothenyi - Pig Hollow (709) Penentelada - Penentel's Camp (709) Seriasdova - Temple of Serias (709)
Sartar: Kingdom of Heroes
Dar - Chief/Tribal King (84) Huscarl - Hall Man (18) Kanvulvretan - Dog Scratching (161) Larnsting - Free/Changer/Liberator (133) Murnulvretan - Cat Scratching (161) Nymie - Counsel (282) Shepelkirt - Poison Blood (104) Tarkarlings - High Free People (76) Wergild - Man Debt (217)
As well as these, the book also mentions some other words. The title of the Prince of Sartar means "first" (84), and that the older version of thane means "horse men" (208).
Also in Sartar, we have the remnant peoples, absorbed into the Vingkotlings. Their names are given meanings, although it's hard to know if any of them are actually in Theyalan or another language. The Nalda Bin at least seem to be related (if purely through Nalda's similarities to Ernalda) and I suspect they may be from the Durevings. The Korsto Viv and Aranto Viv are likely to share a source, given the shared word Viv ("people")
Remnant People
Buf Gart - Hungry Women (SKoH 41) Ched Durkel - Strings (SKoH 41) Jars Antanggi - People of the Shadows (SKoH 41) Karantuel - Cloud Folk (SKoH 41) Korsto Viv - People of the Rivers (SKoH 41) Nalda Bin - Stick Farmers (SKoH 41) Aranto Viv - Axe People (SKoH 41) Eryain Ins - The Blonds (SKoH 41) Forosto Jann - Deadly Archers (SKoH 41)
Sartar Companion
Abylgani - Wrathful Ones (153) Afrasaronafra - The River of River (63) Unani - Pleasant Ones (153)
The Book of Heortling Mythology
Autero - Goldentongue (144) Carl - Free (88) Ches Takal - Chalk Man (45) Golagolar - Fighting Man of the Armies (168) Hara - Beloved (2) Infrendel - Seat of Brass (91) Makla Mann - Unfailing Bondsman (182) Orlanth dovar - Orlanth the Faithful (148) Sevsalsal - Great Poison Breath (168) Tarumath - High Wind (136) Ura - Pleasant One (145) Varanorlanth - Wild Orlanth (37) Venebain - Attacker from Above (169)
Esrolia: The Land of Ten Thousand Goddesses
Besengen - That Big Guy over there (39) Dejess - Lies (21) Desdel - Surprise (30) Dungaria - Mother of the Widow (30) Esrolia - Grainland (21) Ezel - Her Home (14) Irinioori - High Water Mark (23) Kena - Headrest/Pillow (21) Notchet - Everyone (22) Orenvulvretan - Stone Scratching (22) Tereen - Chosen of Ter (23) Terliol - Blessed of Ter (23)
Miscellaneous
Alda Chur - Far Place (Wyrms Footprints #15 40) Meldek - Emptied/Sorcerer (Strangers in Prax 65)
Despite the age of Strangers in Prax, both Emptied and Meldek have been used in modern source material (Sartar: KoH 209, and Sartar Companion 86 respectively) although never explicitly linked together. However, it's likely still valid.
These next three books are no longer canon, but still contained examples of Theyalan words. Several (the spirits/agents of retribution) are used in Sartar: Kingdom of heroes, but untranslated.
Thunder Rebels
-ing - Children of/Descendent of (156) Banumbroling - Wind Fist (85) Belnan - Clodfoot (82) Driman - Heavy (205) Esnan - Earth Thief/Gulper (83) Haruling - Impest (82) Hedkoring - Flint Slinger (83) Manmolaning - Breath Stealer (247) Ohorakoring - Storm Fury (247) Yavorling - Bolter/Jag/Sparker (81)
Storm Tribe
Duro - Win (10) Kara - Draw/Tie (10) Reflarting - Blinder (55) Vanda - Lose (10) Yoskati - Warmth Stealer (55)
Imperial Lunar Handbook 1
Orshil - First Axe (13) Shilkot - Master of Axes (14) Tvengkot - Master of Battles (14)
There's also an article and a post of Jeff's which seem useful. Certainly Ernaldaravandi, Tekravand, Viskuranth, and Viskuvath are used in other places (Thunder Rebels for the first two, and Sartar: Kingdom of Heroes and the Book of Heortling Mythology for the latter)
Babeestervandi - Babeester's Holy Day Ernaldaravandi - Ernalda Holy Day Esrolaravand - Esrola's Holy Day Orlanthharvandar - Orlanth High Holy Day Tekravand - Shroud Holy Day Mahomravand - Mahome's Holy Day/Fire Celebration Voriaravand - Voria's Holy Day
Tarvathlinpor - Place of the High Breath Viskuranth - Son of the Spike Viskuvath - Breath of the Spike
From these, we can determine a few simple building blocks of words:
Ada - Camp (From Penentelada) Afra - River (From Afrasaronafra) Anth - Son/Child (From Viskuranth) Dov - Faith/Holy (From Orlanth dovar and Seriasdova) Hus - Hall (From Huscarl) Kan - Dog (From Kanvulvretan) Kar - Free (From Carl and Tarkarling) Mahom - Fire (From Mahomravand and the goddess Mahome) Murn - Cat (From Murnulvretan and the god Murni) Nald - Farmer (From Nalda Bin, and the goddess Ernalda) Oren - Stone (From Orenvulvretan) Ravand - Celebration/Holy Day (From Mahomravand and a bunch of others) Tar - High (From Tarkarlings, Tarvathlinpor, and Tarumath) Tek - Shroud (From Tekravand, and the goddess Ty Kora Tek) Ulvretan - Scratching/Writing (From Kanvulvretan, Murnulvretan, and Orenvulvretan) Varan - Wild (From Varanorlanth) Vath - Breath (From Tarvathlinpor and Viskuvath) Visku - Spike (From Viskuranth and Viskuvath)
To make a quick note on Anth, although found as Ranth in Viskuranth, -anth is given as a common suffix in Orlanthi names in Sartar: Kingdom of Heroes (26), often found as -lanth or -vanth. It's also found as -antha in Erantha Gor, and Glorantha -- suggesting the term is unisex.
We also have a couple of suffixes:
-een - Chosen of (From Tereen) -ing - Children of/Descendent of (As previously mentioned) -liol - Blessed of (From Terliol) -linpor - Place of (From Tarvathlinpor)