so-

From Old Irish so-, su- (“good”), from Proto-Celtic *su-, from Proto-Indo-European *h₁su-. Cognate with Welsh hy- (“very, easy to”), Ancient Greek εὖ (eû), Sanskrit सु- (su-). Doublet of eo-.

so-

1. very (positive or neutral)

   Synonyms: dea-, deas, maith

2. X-able, easy to X

   Synonym: furasta

• This affix in Irish is added to adjectives denoting attributes of ability as well as positive attributes. It lenites the word to which it attaches.
• When it means very, so- acts like an adverb:

  ‎so- + ‎blasta (“tasty”) → ‎so-bhlasta (“very tasty”)

• When it means -able, so- acts like an plain affix:

  ‎so- + ‎briste (“broken”) → ‎sobhriste (“breakable”)

  ‎so- + ‎déanta (“done”) → ‎sodhéanta (“doable”)

• do-
• ró-

Irish mutation
Radical	Lenition	Eclipsis
so-	sho- after an, tso-	not applicable
Note: Some of these forms may be hypothetical. Not every possible mutated form of every word actually occurs.

• Ó Dónaill, Niall (1977) “so-”, in Foclóir Gaeilge–Béarla, Dublin: An Gúm, →ISBN
• Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “2 so, su”, in eDIL: Electronic Dictionary of the Irish Language

From Latin sub- (“under”).

• IPA^(key): /so/
• Hyphenation: so-

so-

1. under, beneath

   ‎so- + ‎gola (“throat”) → ‎soggolare (“to fit with a wimple”)

   ‎so- + ‎reggere (“to bear; to hold”) → ‎sorreggere (“to support, sustain”)

2. used in the formation of verbs where the root action is attenuated

   ‎so- + ‎friggere (“to fry”) → ‎soffriggere (“to fry slowly with moderate heat”)

   ‎so- + ‎bollire (“to boil”) → ‎sobbollire (“to simmer”)

   ‎so- + ‎fermare (“to stop”) → ‎soffermare (“to linger”)

• It always causes gemination of an initial single consonant.

From Old Irish so, su.

so-

1. X-able, easily Xed

• Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “2 so, su”, in eDIL: Electronic Dictionary of the Irish Language

From Latin sub-.^[1][2] Doublet of sub-.

so-

1. sub- (under, beneath)

   Synonym: sub-

Inherited from Proto-Slavic *sǫ-.

so-

1. con-, co- (with, together, jointly)

• IPA^(key): /so/ [so]
• Syllabification: so-

so-

1. sub-

   Synonym: sub-

• “so-”, in Diccionario de la lengua española [Dictionary of the Spanish Language] (in Spanish), online version 23.7, Royal Spanish Academy [Spanish: Real Academia Española], 2023 November 28