What is the meaning of ?

The hiragana syllable (de). Its equivalent in katakana is (de).

at: indicating a location at which something happens

with, by, using: indicating the means by or with which something happens

(Can we verify this sense?) in: indicating the containing by something

indicating the following sentence is a consequence of something previously stated: and then; therefore

is/am/are ... and: the て-form or conjunctive form of (da)

Attaches to the 未然形 (mizenkei, irrealis or incomplete form) of verbs to form the negative conjunctive, equivalent to the modern ないで (-naide) or ずに (-zuni).

sentence-ending particle signifying emphasis

Source: wiktionary.org