If the past participle of "say" is "said", and "lay" is "laid", why the one of "stay" is not "staid"?

I know about the word "staid". Does the past participle of "stay" is "stayed" to avoid confusion with this word?

Or the "staid" past participle existed at some time, but it was supplanted by "stayed", like "dreamed" is replacing "dreamt"?

Solution 1:

You seem to be trying to use two irregularly spelled words as a basis for figuring out (or for explaining) the spelling of other words. That's a recipe for confusion. "Stayed" is the regular, expected spelling for the past participle and past tense of "stay"; likewise, the past participles of bay, pray, play, array, delay, decay, spray, display, sway end in -ayed and not in -aid. They are not spelled with -ayed to avoid confusion with other words; they are spelled with -ayed because most past participles are spelled by adding -ed to the base form of the word.

The past participle of the verb stay was spelled many different ways in the past. The Oxford English Dictionary gives the following list:

ME–17 stayd, 15 Scottish stayit, stayet, steyit, 15–16 stayde, staied, staide, 15–18 staid, 15– stayed.

Related question: Why is "say" spelled differently for "said" and "says"?