Heard spelling

thirse

Spelled thyrse. y doing the work of i

The vowel sounds like the i in first.

It does, and it is written y.

Greek upsilon comes into English as y and then behaves like any other English vowel letter, which is to say unpredictably. Myrrh, myrtle and thyrse all take that y and all say a plain short vowel with an r behind it.

Say

THURSS, rhyming with verse

Letters

T-H-Y-R-S-E