  Linear magnetoelectric effect is an attractive phenomenon in condensed
matters and provides indispensable technological functionalities. Here a
colossal linear magnetoelectric effect with diagonal component alfa_33 reaching
up to ~480 ps/m is reported in a polar magnet Fe2Mo3O8, and this effect can
persist in a broad range of magnetic field (~20 T) and is orders of magnitude
larger than reported values in literature. Such an exceptional experimental
observation can be well reproduced by a theoretical model affirmatively
unveiling the vital contributions from the exchange striction, while the sign
difference of magnetocrystalline anisotropy can also be reasonably figured out.
