1. semi-trailer, (USA, Canada) semi, (UK) artic trailer (a trailer without front axle and with wheels only at the trailing end, designed to be pulled via a pivoting arrangement which also partially supports its weight.)

2. (USA, Canada) semi-truck, 18-wheeler, eighteen-wheeler, semi-trailer truck, tractor-trailer, semi, big rig ; (UK) articulated lorry, artic, HGV, LGV, juggernaut, jugger (a semi-trailer plus the truck or tractor pulling it) (Bolivia, Costa Rica, Ecuador, Honduras, Nicaragua, Mexico, Panama, Peru, Puerto Rico, Spain)

3. trailer (vehicle) (rare)

4. trailer (preview)