It is a philosophical as much as a psychological enigma. Yes, we might define freedom as the absence of fear but any definition by counterfactual (or negation) is always and already intimately shaped by – and anchored upon – an inadvertent dependence on that which it asserts that it is not.
In the above sense, freedom can only ever truly be of something utterly unconstrained by binary antitheses, polar definitions or difference. Granted, it is a soul-warming mnemonic to dream of freedom from fear, from suffering and an omnipresent spectre of personal extinction but the trick is not to become fixated on the definition.
Just as melody and rhythm in music is defined as much by the absence of sound as by its presence, freedom is also conceivable as the presence of an absence of all constraint, boundary or definition. It is a subtle concept and also one for which language (as much as its ordered grammars of cognition) is quite poorly-suited to engage.