-og

From -o- (linking vowel) +‎ -g (frequentative suffix).

• IPA^(key): [oɡ]

-og

1. (frequentative suffix) Added to a stem - often an onomatopoeia - to form a verb expressing a (quickly) repeating or continuous action.

   vacog (“to chatter - to shut and open the mouth quickly in the cold”)

   ‎mosoly (“smile”) + ‎-og → ‎mosolyog (“to smile”)

• (frequentative suffix) Variants:

  -g is added to words ending in a vowel

  -og is added to some back-vowel words

  -ag is added to other back-vowel words

  -eg is added to unrounded front-vowel words

  -ög is added to rounded front-vowel words

• Appendix:Hungarian suffixes

• -iog

From Middle Welsh -awc, from Proto-Brythonic *-ọg, from Proto-Celtic *-ākos, from Proto-Indo-European *-eh₂kos, *-eh₂ḱos, from a-stem suffix *-eh₂ + adjectival suffix *-kos, *-ḱos. Akin to Cornish -ek, Breton -eg, Irish -ach, Scottish Gaelic -ach, Manx -agh, Latin -ācus, -īcus and English -y.

• IPA^(key): /ɔɡ/

-og

1. adjectival suffix often indicating an abundance of the root

   ‎carreg (“stone”) + ‎-og → ‎caregog (“stony”)

   ‎twll (“hole”) + ‎-og → ‎tyllog (“porous”)

   ‎gallu (“ability”) + ‎-og → ‎galluog (“capable”)

   ‎enw (“name”) + ‎-og → ‎enwog (“famous”)

2. noun suffix indicating person, creature or object characterised by root

   ‎perchen (“to own”) + ‎-og → ‎perchennog (“owner”)

   ‎march (“stallion, horse”) + ‎-og → ‎marchog (“knight, horserider”)

   ‎draen (“thorn(s)”) + ‎-og → ‎draenog (“hedgehog”)

   ‎ysgyfarn (“ear”) + ‎-og → ‎ysgyfarnog (“hare”)

   ‎clust (“ear”) + ‎-og → ‎clustog (“cushion, bolster”)

R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke et al., editors (1950–present), “-og”, in Geiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies