to throw or lay something onto something; to lay hands on a person, that is, to seize or arrest
At its root the word means to throw or set one thing on top of another: a patch onto a worn coat, cloaks onto the back of a donkey, a hand onto the handle of a plow. The action is a placing, but with a hint of the toss or the reach behind it, since it is built from the ordinary verb for throwing.
Its most common use in the New Testament is the fixed expression "to lay hands on" someone. This is almost never a gentle or ceremonial touch. It is the move of an arrest or an assault: soldiers and officials laying hold of Jesus, of the apostles, or of Paul. Often the whole point is that hands could not yet be laid on Jesus, because his hour had not come. A close relative, πιάζω, names the actual catching and holding of the prisoner, while this word names the outward move of reaching for him.
The same verb can also mean to fasten or force something onto a person in a figurative way, as when Paul says he is not trying to throw a restraint over anyone.