My daughters name is Teagan. After much research, I found that it is derived from the name Tadhg which is prn. TAYG,therefore the diminutive form would be prn. Tay-gen.In fact an older woman from Ireland whom I work with agreed this was the correct way to pronounce it.I think people see the first three letters and say tea like the beverage.When people argue with me, I remind them it rhymes with Reagan,the T instead of R doesn't change the pronounciation!Also the spelling Tegan(as someone pointed out) comes from the unrelated(female) welsh name Tegwen meaning 'beautiful,attractive' so while Teagan is a unisex name Tegan is strictly feminine . I hope this helps!