In eo quod amatur, aut non laboratur, aut et labor amatur - There is no fatigue when is something you love, or you love that fatigue
In esse - In being (Philosophical term - Saint Thomas Aquinas - In existence - Before we are born we are in In posse. After we are born, we are In esse)
In extenso - At full length
In extremis - In the extreme (Legal Term - At the point of death, or in extreme circumstances - Medical Term - patient who is in critical condition, about to die)
In facie ecclesiae - At the face of the church (Ecclesiastical term - e.g. a wedding)
In fieri - In process (Pending)
In fine - At the end
In flagranti delicto - [Caught] in the act of the offence (Legal term - Caught with the hands in the cookie jar)
In fraganti - In the act (Legal term - At the moment of committing the crime)
In fragantia poesis abditus - In fragrance hidden poetry
In globo - Globally (In mass)
In hoc signo vinces - In this sign you will conquer (The Roman Emperor Constantine became a Christian after he dreamed of a cross and those words in Greek: Εν Τουτω Νικα. He won many battles after his soldiers painted crosses in their armors and shields)
In Humilitate Vincis - In humility you will conquer (Motto del Rugby Club of the Metropolitan University in Caracas, Venezuela)
In ictu oculi - In the blink of an eye
In illo tempore - At that time
In integrum - Integral (Legal term)
In itinere - During the journey (Legal term - Something that happens during the fact)
In ius vocatio - Call for justice (Legal term)
In lacrimas Liqui - Break and cry
In Libertatem Vocati - You have been called unto liberty (Vulgate - Galatians 5, 13)
In limine litis - At the beginning of the process Legal term)
In loco parentis - In lieu of parents (Legal Term - often used in Family Court to assign parental responsibilities often on non-biological parental substitutes/parties - Thank you: crj)
In Lumine Sapientia - Wisdom is in the light (Motto of the Almeria University in Spain)
In maculisi - Immaculate
In magnis et voluisse satis est - To once have wanted is enough in great deeds (Propertius)