What is the meaning of Thou?

Nominative singular of ye (you).

To address (a person) using the pronoun thou, especially as an expression of contempt or familiarity.

To use the word thou.

A unit of length equal to one-thousandth of an inch (25.4 µm).

A thousand, especially a thousand of some currency (dollars, pounds sterling, etc.).

Misspelling of though.

Misspelling of though.

Alternative form of þou

thou

thou, you

Source: wiktionary.org