The phrase "big as life" describes something or someone that is prominent, bold, or impossible to ignore. However, there are several antonyms for this expression that convey the opposite meaning. For instance, "small as a mouse" or "tiny as a pin" suggests something that is barely noticeable or easily overlooked. "Insignificant," "insubstantial," or "trivial" convey a sense of smallness or unimportance. On the other hand, "ambiguous," "obscure," or "unclear" implies something that is not immediately apparent or easy to perceive. In summary, the antonyms for "big as life" span across a range of words that indicate smallness, insignificance, or ambiguity.