1. Given without an equivalent or recompense; conferred without valuable consideration; granted without pay, or without claim or merit; not required by justice.
We mistake the gratuitous blessings of Heaven for the fruits of our own industry. --L'Estrange.
2. Not called for by the circumstances; without reason, cause, or proof; adopted or asserted without any good ground; as, a gratuitous assumption.
Acts of gratuitous self-humiliation. --De Quincye.
-- Gra*tu*i*tous*ly, adv. -- Gra*tu*i*tous*ness, n.
adv : in an uncalled-for manner; "he insulted us gratuitously"