"I work in my office."
Translation:Oibrím i m'oifig.
Go raibh maith agat as ucht do chabhrú. I had to do more digging to find out why 'tiomáin' doesn't behave in this way as well. What I discovered in my friend's college notes was that 1st conjugation verbs include those with monosyllabic roots as well as two-syllable roots ending in '-áin', 'áil' and '-óil', whereas the 2nd conjugation includes two-syllable roots ending in '-igh' and those that have 'i' or 'ai' in their second syllable: this covers 'labhair' and 'oscail' as well as 'inis' and 'imir'.