A puppy looking out of a window.
An example of something that would be described as plaintive would be the sad whimper of a puppy whose owners have just left him all alone.
Origin of plaintiveMiddle English pleintif from Old French plaintif: see plaintiff
Origin of plaintiveMiddle English plaintif from Old French aggrieved, lamenting from plaint complaint ; see plaint .
(comparative more plaintive, superlative most plaintive)
From Old French plaintif (“aggrieved, lamenting"), from plainte (“lament, complaint"); see plaint.