To constrain someone by force or by social, moral or legal means.
To be indebted to someone.
To do (someone) a service or favour (hence, originally, creating an obligation).
To cause to fail; to frustrate, to prevent.
A seat across a boat on which a rower may sit.
An act of thwarting; something which thwarts; a hindrance, an obstacle.
A brace, perpendicular to the keel, that helps maintain the beam (“breadth”) of a marine vessel against external water pressure and that may serve to support the rail.
Placed or situated across something else; cross, oblique, transverse.