だで

is, am, are

→ だ
だ Plain copula (nonpast) + で Te-form (conjunctive)
auxiliary · informal Rare #40,643
is, am, are Colloquial regional dialect, especially in central Japan; used as an assertive sentence ending. It can also mean “because” in some contexts.
JA: 今日は休みだで。
EN: Today is a day off.
Conjugation of だ

年だでな

I'm getting old, you know.

— 七人の侍 (1954)

その通りだであんたは?

That's right. How about you?

— 罪人たち (2025)

彼は私を招いた男だでも彼を議会で侮辱したサンドイッチよりは重宝だ

He’s the man who invited me, but he’s more useful than the sandwich that insulted him in parliament.

— オッペンハイマー (2023)