sayyoudaoicibaDictYouDict[say 词源字典]
say: [OE] Say is part of a widespread Germanic family of ‘say’-verbs, which also contains German sagen, Dutch zeggen, Swedish säga, and Danish sige. These point back to a common Germanic ancestor *sagjan, which was descended from the Indo-European base *seq-. This originally signified ‘point out’, but evolved to ‘say’, and it also lies behind Lithuanian sakýti, Latvian sacīt, Welsh eb, and Latin inquit, all of which mean ‘say’.
=> saga, saw[say etymology, say origin, 英语词源]
say (v.)youdaoicibaDictYouDict
Old English secgan "to utter, inform, speak, tell, relate," from Proto-Germanic *sagjanan (cognates: Old Saxon seggian, Old Norse segja, Danish sige, Old Frisian sedsa, Middle Dutch segghen, Dutch zeggen, Old High German sagen, German sagen "to say"), from PIE *sokwyo-, from root *sekw- (3) "to say, utter" (cognates: Hittite shakiya- "to declare," Lithuanian sakyti "to say," Old Church Slavonic sociti "to vindicate, show," Old Irish insce "speech," Old Latin inseque "to tell say").

Past tense said developed from Old English segde. Not attested in use with inanimate objects (clocks, signs, etc.) as subjects before 1930. You said it "you're right" first recorded 1919; you can say that again as a phrase expressing agreement is recorded from 1942, American English. You don't say (so) as an expression of astonishment (often ironic) is first recorded 1779, American English.
say (n.)youdaoicibaDictYouDict
"what someone says," 1570s, from say (v.). Meaning "right or authority to influence a decision" is from 1610s. Extended form say-so is first recorded 1630s. Compare Old English secge "speech."