What is the Greek letter equal to th?

There is no Greek letter that is equal to "th". The sound "th" is not represented by a single Greek letter.

The sound "th" can be represented in different ways in Greek, depending on the specific pronunciation:

* θ (theta): This letter represents the voiceless dental fricative, which is similar to the "th" sound in "thin" or "think".

* δ (delta): This letter represents the voiced dental fricative, which is similar to the "th" sound in "this" or "that".

It's important to remember that these are just approximations of the "th" sound, and they may not be identical to the way the sound is pronounced in English.