Liquid, fluid are comparable both as adjectives meaning composed of particles that move easily and flowingly and change their relative position without any perceptible break in their continuity and as nouns denoting a substance composed of such particles.
Both terms imply an opposition to solid, but liquid is the more restricted in its application, for the term implies the flow characteristic of water and refers only to substances which, like water, have a definite volume but no independent form except such as is temporarily given by their container.
Fluid, on the other hand, implies flow of any sort and is applicable not only to all liquids but also to gases, which, unlike liquids, have neither independent volume nor shape.
Fluid is especially appropriate for referring to a substance that is highly viscous or to one liquefied (as by melting, dissolving, or saturating with water).
In extended use fluid is opposed to rigid, fixed, unchangeable.
Liquid, on the other hand, often implies an opposition to harshness, but it sometimes implies transparency or extreme softness or both. In financial circles, where both terms are used, fluid may distinctively apply to money or funds that are not permanently invested or that are constantly in circulation, but more often the terms are used interchangeably to imply the quality or condition of assets that are in the form of money or are easily convertible into money and are therefore readily available for another use.