Middle English sori, from Old English sarig "distressed, grieved, full of sorrow" (not found in the physical sense of "sore"), from Proto-Germanic *sairiga- "painful" (source also of Old Saxon serag, Middle Dutch seerigh "sore; sad, sorry," Dutch zeerig "sore, full of sores," Old High German serag, Swedish sårig "sore, full of sores"), from *sairaz "pain" (physical and mental); related to *saira- "suffering, sick, ill" (see sore (adj.)).
The spelling shift from -a- to -o- is by influence of (unrelated) sorrow. Specifically as "repentant, remorseful, contrite" by c. 1200. The meaning "wretched, worthless, poor" is recorded by mid-13c. Simple sorry in an apologetic sense (short for I'm sorry) is suggested by 1834; the phrase sorry about that seems to have been popularized mid-1960s by U.S. TV show "Get Smart." To be sorry for (something) is in late Old English. Related: Sorrily; sorriness.
-ish
adjectival word-forming element, Old English -isc "of the nativity or country of," in later use "of the nature or character of," from Proto-Germanic suffix *-iska- (cognates: Old Saxon -isk, Old Frisian -sk, Old Norse -iskr, Swedish and Danish -sk, Dutch -sch, Old High German -isc, German -isch, Gothic -isks), cognate with Greek diminutive suffix -iskos. In its oldest forms with altered stem vowel (French, Welsh). The Germanic suffix was borrowed into Italian and Spanish (-esco) and French (-esque). Colloquially attached to hours to denote approximation, 1916.
The -ish in verbs (abolish, establish, finish, punish, etc.) is a mere terminal relic from the Old French present participle.