Ant. Powerless, inefficient, impotent.
Omniscient. All-knowing, infallible, all-wise.
Ant. Shortsighted, fallible, ignorant.
One. Single, individual, solitary, certain, undivided, common, united, unitary.
Ant. Many, several; few.
Onerous. Burdensome, oppressive, heavy, toilsome, difficult, laborious, responsible.
Ant. Light, easy, trivial.
Only, ad. Solely, singly, exclusively, merely, barely, wholly.
Ant. Among, amongst, together, collectively.
Only, a. Single, sole, alone, preëminent, chief.