Sanyas and yoga
Krishna in the Bhagwat Gita says that the one who is Sanyasi is yogi too. And he then goes on speaking difference between the two i.e., that what is sanyas and what is yoga.
He very beautifully explains sanyas as a journey on the train. This ( train journey) is a state of voluntary detachment from the world I.e., a passenger buys a ticket, leaves the local station and boards a train. Upon buying a ticket he knows the destination and sits in a coach comfortably and sees the world outside through windows of its choice but cannot jump out of it and cannot go back to a turbulent world. Train carries all passengers to their chosen destination.
At the end of sanyas comes the yoga. Yoga is a state which is like reaching destination where you leave the coach or body which housed you so long, without even looking at it once and jump out to your great great great great great .. grandparents who came there at platform and waited to receive you with open arms.
Nyas means home ( not any house). There was no train in those days so Krishna used a term nyas for home or body. SaNyas means "with body" or sitting in body or house (or train as in my example) but not attached with dependency on turbulent world. Sanyas means " a person seated on a train and traveling to its destination peaceful ". Nya also means justice or rule bound home or train using high technical precision. Home or nyas is trustworthy environment and therefore nyay means trust or natural justice.
Note: Because of lack of knowledge in English, in India, courts are incorrectly called "nyayalay". This is a gross violation of spirit of this word. Courts means a ground for battle or opponents who collide. Courts are a Greek term for coliseum or places of collision.
Train has different class of coaches. Therefore sanyasi are of different types. " chatur varna maya srishtim gun karm vibhag shah". There are four divisions (vibhag) of work ( karm) based on various characters ( gun) of people. Varna means color or personality. Work while journey in the world to our chosen destination has four divisions and each one has distinct personality. This varna is not by birth but work can be anytime changed by changes in character.
Brahman are drivers and technical staff who focus only on train operations. Chhatria are safety and security and housekeeping staff. Vaishya are catering and food supply. Shudra are passengers who pay for tickets. This way all passengers live together and pursue their journey in the world but remain detached with the world and its possessiveness. All of them work different but have similar destination and are interdependent.