thyr-
prefix
 (before a vowel) a variant form of thyro-
thyro- or (before a vowel) thyr-
combining form
thyroid
⇒ 
thyrotoxicosis
⇒ 
thyrotropin
☞ thyro-
thyr-a combining form of thyroid, as in thyroxine.
Also, (before consonants), thyro-.
thyr-
combining form
or thyro-
thyrotoxicosis
thyroxine
combining form
or thyro-
 ETYMOLOGY  thyroid
: thyroidthyrotoxicosis
thyroxine
thyr-
combining form 
or thyro-
Etymology: thyroid 
1. : thyroid 
< thyrasthenia >
2. : thyroid and 
< thyroarytenoid >
or thyro-
1.
< thyrasthenia >
2.
< thyroarytenoid >