To tug is to forcefully pull or drag something. You might need your sister's help to tug your knee-high boots off at the end of a long day.
A child might tug at his parent's arm and a commuter might tug a rolling suitcase behind her as she enters a subway car. Something else that tugs is a tugboat — and tug is a common nickname for these boats that are designed to pull (or push) other vessels. Tug and tow share the same root word meaning "to pull" or "to lead."